refactor(aibridge): move shared mock helpers to testutil (#25999)

Moves the shared aibridge mock test helpers (`MockUpstream`, `MockServerProxier`, `StubToolCaller`, and the `NewFixtureResponse`/`NewFixtureToolResponse` constructors) out of `aibridge/internal/integrationtest` into `aibridge/internal/testutil`, and exports them.

This lets the per-interceptor test packages (`messages`, `chatcompletions`, `responses`) reuse one set of mocks instead of each redefining its own. The symbols are exported and call sites updated, with no behavior change.

Closes: https://linear.app/codercom/issue/AIGOV-397/move-mockserverproxier-into-a-shared-testutil-package

> [!NOTE]
> Initially generated by Claude Opus 4.7, modified and reviewed by @ssncferreira

aibridge/intercept/chatcompletions/blocking_internal_test.go

@@ -1,7 +1,6 @@
 package chatcompletions
 
 import (
-	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -10,7 +9,6 @@ import (
 	"testing"
 
 	"github.com/google/uuid"
-	mcplib "github.com/mark3labs/mcp-go/mcp"
 	"github.com/openai/openai-go/v3"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -450,10 +448,10 @@ func TestBlockingInterception_AgenticLoopFailover(t *testing.T) {
 
 			// Mock proxy with a tool the upstream's tool_use
 			// response will reference.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",
@@ -483,41 +481,3 @@ func TestBlockingInterception_AgenticLoopFailover(t *testing.T) {
 		})
 	}
 }
-
-// mockServerProxier is a test implementation of mcp.ServerProxier.
-type mockServerProxier struct {
-	tools []*mcp.Tool
-}
-
-func (*mockServerProxier) Init(context.Context) error {
-	return nil
-}
-
-func (*mockServerProxier) Shutdown(context.Context) error {
-	return nil
-}
-
-func (m *mockServerProxier) ListTools() []*mcp.Tool {
-	return m.tools
-}
-
-func (m *mockServerProxier) GetTool(id string) *mcp.Tool {
-	for _, t := range m.tools {
-		if t.ID == id {
-			return t
-		}
-	}
-	return nil
-}
-
-func (*mockServerProxier) CallTool(context.Context, string, any) (*mcplib.CallToolResult, error) {
-	return nil, nil //nolint:nilnil // mock: no-op implementation
-}
-
-// stubToolCaller is a minimal mcp.ToolCaller that returns a fixed
-// text result, so the agentic continuation can proceed.
-type stubToolCaller struct{}
-
-func (stubToolCaller) CallTool(_ context.Context, _ mcplib.CallToolRequest) (*mcplib.CallToolResult, error) {
-	return mcplib.NewToolResultText("tool result"), nil
-}

aibridge/intercept/chatcompletions/streaming_internal_test.go

@@ -580,10 +580,10 @@ func TestStreamingInterception_AgenticLoopFailover(t *testing.T) {
 			// Mock proxy with a tool the upstream's tool_calls
 			// chunks will reference. The stub caller returns a
 			// fixed text result.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",

aibridge/intercept/messages/base_internal_test.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/anthropics/anthropic-sdk-go"
 	"github.com/anthropics/anthropic-sdk-go/shared/constant"
-	mcpgo "github.com/mark3labs/mcp-go/mcp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/tidwall/gjson"
@@ -17,6 +16,7 @@ import (
 
 	"cdr.dev/slog/v3"
 	"github.com/coder/coder/v2/aibridge/config"
+	"github.com/coder/coder/v2/aibridge/internal/testutil"
 	"github.com/coder/coder/v2/aibridge/keypool"
 	"github.com/coder/coder/v2/aibridge/mcp"
 	"github.com/coder/coder/v2/aibridge/utils"
@@ -476,7 +476,7 @@ func TestInjectTools_CacheBreakpoints(t *testing.T) {
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tools":[`+
 				`{"name":"existing_tool","type":"custom","input_schema":{"type":"object","properties":{}},"cache_control":{"type":"ephemeral"}}]}`),
-			mcpProxy: &mockServerProxier{tools: nil},
+			mcpProxy: &testutil.MockServerProxier{Tools: nil},
 			logger:   slog.Make(),
 		}
 
@@ -496,8 +496,8 @@ func TestInjectTools_CacheBreakpoints(t *testing.T) {
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tools":[`+
 				`{"name":"existing_tool","type":"custom","input_schema":{"type":"object","properties":{}},"cache_control":{"type":"ephemeral"}}]}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{ID: "injected_tool", Name: "injected", Description: "Injected tool"},
 				},
 			},
@@ -525,8 +525,8 @@ func TestInjectTools_CacheBreakpoints(t *testing.T) {
 			reqPayload: mustMessagesPayload(t, `{"tools":[`+
 				`{"name":"tool_with_cache_1","type":"custom","input_schema":{"type":"object","properties":{}},"cache_control":{"type":"ephemeral"}},`+
 				`{"name":"tool_with_cache_2","type":"custom","input_schema":{"type":"object","properties":{}}}]}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{ID: "injected_tool", Name: "injected", Description: "Injected tool"},
 				},
 			},
@@ -554,8 +554,8 @@ func TestInjectTools_CacheBreakpoints(t *testing.T) {
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tools":[`+
 				`{"name":"existing_tool_no_cache","type":"custom","input_schema":{"type":"object","properties":{}}}]}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{ID: "injected_tool", Name: "injected", Description: "Injected tool"},
 				},
 			},
@@ -583,7 +583,7 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tool_choice":{"type":"auto"}}`),
-			mcpProxy:   &mockServerProxier{tools: nil}, // No tools to inject.
+			mcpProxy:   &testutil.MockServerProxier{Tools: nil}, // No tools to inject.
 			logger:     slog.Make(),
 		}
 
@@ -600,8 +600,8 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
 			},
 			logger: slog.Make(),
 		}
@@ -619,8 +619,8 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tool_choice":{"type":"auto"}}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
 			},
 			logger: slog.Make(),
 		}
@@ -638,8 +638,8 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tool_choice":{"type":"any"}}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
 			},
 			logger: slog.Make(),
 		}
@@ -657,8 +657,8 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tool_choice":{"type":"tool","name":"specific_tool"}}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
 			},
 			logger: slog.Make(),
 		}
@@ -676,8 +676,8 @@ func TestInjectTools_ParallelToolCalls(t *testing.T) {
 
 		i := &interceptionBase{
 			reqPayload: mustMessagesPayload(t, `{"tool_choice":{"type":"none"}}`),
-			mcpProxy: &mockServerProxier{
-				tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
+			mcpProxy: &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{{ID: "test_tool", Name: "test", Description: "Test"}},
 			},
 			logger: slog.Make(),
 		}
@@ -936,36 +936,6 @@ func mustMessagesPayload(t *testing.T, requestBody string) RequestPayload {
 	return payload
 }
 
-// mockServerProxier is a test implementation of mcp.ServerProxier.
-type mockServerProxier struct {
-	tools []*mcp.Tool
-}
-
-func (*mockServerProxier) Init(context.Context) error {
-	return nil
-}
-
-func (*mockServerProxier) Shutdown(context.Context) error {
-	return nil
-}
-
-func (m *mockServerProxier) ListTools() []*mcp.Tool {
-	return m.tools
-}
-
-func (m *mockServerProxier) GetTool(id string) *mcp.Tool {
-	for _, t := range m.tools {
-		if t.ID == id {
-			return t
-		}
-	}
-	return nil
-}
-
-func (*mockServerProxier) CallTool(context.Context, string, any) (*mcpgo.CallToolResult, error) {
-	return nil, nil //nolint:nilnil // mock: no-op implementation
-}
-
 func TestFilterBedrockBetaFlags(t *testing.T) {
 	t.Parallel()
 

aibridge/intercept/messages/blocking_internal_test.go

@@ -443,10 +443,10 @@ func TestBlockingInterception_AgenticLoopFailover(t *testing.T) {
 
 			// Mock proxy with a tool the upstream's tool_use
 			// response will reference.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",

aibridge/intercept/messages/streaming_internal_test.go

@@ -1,7 +1,6 @@
 package messages
 
 import (
-	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -10,7 +9,6 @@ import (
 	"testing"
 
 	"github.com/google/uuid"
-	mcplib "github.com/mark3labs/mcp-go/mcp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel"
@@ -367,14 +365,6 @@ data: {"type":"message_stop"}
 `
 )
 
-// stubToolCaller is a minimal mcp.ToolCaller that returns a fixed
-// text result, so the agentic continuation can proceed.
-type stubToolCaller struct{}
-
-func (stubToolCaller) CallTool(_ context.Context, _ mcplib.CallToolRequest) (*mcplib.CallToolResult, error) {
-	return mcplib.NewToolResultText("tool result"), nil
-}
-
 // TestStreamingInterception_AgenticLoopFailover covers the
 // scenarios that span an agentic-loop continuation: the initial
 // client request and the subsequent tool-call continuation can
@@ -537,10 +527,10 @@ func TestStreamingInterception_AgenticLoopFailover(t *testing.T) {
 			// Mock proxy with a tool the upstream's tool_use event
 			// will reference. The stub caller returns a fixed
 			// text result.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",

aibridge/intercept/responses/blocking_internal_test.go

@@ -1,7 +1,6 @@
 package responses
 
 import (
-	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -10,7 +9,6 @@ import (
 	"testing"
 
 	"github.com/google/uuid"
-	mcplib "github.com/mark3labs/mcp-go/mcp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel"
@@ -440,10 +438,10 @@ func TestBlockingResponsesInterceptor_AgenticLoopFailover(t *testing.T) {
 
 			// Mock proxy with a tool the upstream's function_call
 			// response will reference.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",
@@ -473,41 +471,3 @@ func TestBlockingResponsesInterceptor_AgenticLoopFailover(t *testing.T) {
 		})
 	}
 }
-
-// mockServerProxier is a test implementation of mcp.ServerProxier.
-type mockServerProxier struct {
-	tools []*mcp.Tool
-}
-
-func (*mockServerProxier) Init(context.Context) error {
-	return nil
-}
-
-func (*mockServerProxier) Shutdown(context.Context) error {
-	return nil
-}
-
-func (m *mockServerProxier) ListTools() []*mcp.Tool {
-	return m.tools
-}
-
-func (m *mockServerProxier) GetTool(id string) *mcp.Tool {
-	for _, t := range m.tools {
-		if t.ID == id {
-			return t
-		}
-	}
-	return nil
-}
-
-func (*mockServerProxier) CallTool(context.Context, string, any) (*mcplib.CallToolResult, error) {
-	return nil, nil //nolint:nilnil // mock: no-op implementation
-}
-
-// stubToolCaller is a minimal mcp.ToolCaller that returns a fixed
-// text result, so the agentic continuation can proceed.
-type stubToolCaller struct{}
-
-func (stubToolCaller) CallTool(_ context.Context, _ mcplib.CallToolRequest) (*mcplib.CallToolResult, error) {
-	return mcplib.NewToolResultText("tool result"), nil
-}

aibridge/intercept/responses/streaming_internal_test.go

@@ -484,10 +484,10 @@ func TestStreamingResponsesInterceptor_AgenticLoopFailover(t *testing.T) {
 			// Mock proxy with a tool the upstream's function_call
 			// response will reference. The stub caller returns a
 			// fixed text result.
-			proxy := &mockServerProxier{
-				tools: []*mcp.Tool{
+			proxy := &testutil.MockServerProxier{
+				Tools: []*mcp.Tool{
 					{
-						Client:     stubToolCaller{},
+						Client:     testutil.StubToolCaller{},
 						ID:         "test_tool",
 						Name:       "test_tool",
 						ServerName: "coder",

aibridge/internal/integrationtest/apidump_internal_test.go

@@ -121,7 +121,7 @@ func TestAPIDump(t *testing.T) {
 
 			// Setup mock upstream server.
 			fix := fixtures.Parse(t, tc.fixture)
-			srv := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			srv := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			// Create temp dir for API dumps.
 			dumpDir := t.TempDir()

aibridge/internal/integrationtest/bridge_internal_test.go

@@ -89,7 +89,7 @@ func TestAnthropicMessages(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, fixtures.AntSingleBuiltinTool)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -139,7 +139,7 @@ func TestAnthropicMessages(t *testing.T) {
 				assert.Equal(t, "read the foo file", promptUsages[0].Prompt)
 
 				// Verify PRM attribution is NOT present on non-Bedrock Anthropic requests.
-				received := upstream.receivedRequests()
+				received := upstream.ReceivedRequests()
 				require.Len(t, received, 1)
 				ua := received[0].Header.Get("User-Agent")
 				assert.NotContains(t, ua, "sdk-ua-app-id",
@@ -161,9 +161,9 @@ func TestAnthropicMessages(t *testing.T) {
 		t.Cleanup(cancel)
 
 		fix := fixtures.Parse(t, fixtures.AntSingleInjectedToolNoPreamble)
-		upstream := newMockUpstream(ctx, t,
-			newFixtureResponse(fix),
-			newErrorResponse(http.StatusInternalServerError),
+		upstream := testutil.NewMockUpstream(ctx, t,
+			testutil.NewFixtureResponse(fix),
+			testutil.NewErrorResponse(http.StatusInternalServerError, ""),
 		)
 
 		mockMCP := setupMCPForTest(t, defaultTracer)
@@ -274,7 +274,7 @@ func TestAnthropicMessagesModelThoughts(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -340,7 +340,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, fixtures.AntSingleBuiltinTool)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				// We define region here to validate that with Region & BaseURL defined, the latter takes precedence.
 				bedrockCfg := &config.AWSBedrock{
@@ -373,7 +373,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 
 				// Verify that Bedrock-specific model name was used in the request to the mock server
 				// and the interception data.
-				received := upstream.receivedRequests()
+				received := upstream.ReceivedRequests()
 				require.Len(t, received, 1)
 
 				// The Anthropic SDK's Bedrock middleware extracts "model" and "stream"
@@ -471,7 +471,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 					t.Cleanup(cancel)
 
 					fix := fixtures.Parse(t, fixtures.AntSimpleBedrock)
-					upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+					upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 					bCfg := &config.AWSBedrock{
 						Region:          "us-west-2",
@@ -499,7 +499,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 					_, err = io.ReadAll(resp.Body)
 					require.NoError(t, err)
 
-					received := upstream.receivedRequests()
+					received := upstream.ReceivedRequests()
 					require.Len(t, received, 1)
 					body := received[0].Body
 
@@ -561,7 +561,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 		// Mock Bedrock endpoint (simulates AWS). The OnRequest callback
 		// re-signs the received request using only the declared
 		// SignedHeaders and stores whether the signatures match.
-		fixResp := newFixtureResponse(fix)
+		fixResp := testutil.NewFixtureResponse(fix)
 		fixResp.OnRequest = func(r *http.Request, body []byte) {
 			authHeader := r.Header.Get("Authorization")
 			// Passthrough requests have no SigV4 auth; skip verification.
@@ -602,7 +602,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 			recomputedSig := extractSigV4Field(verifyReq.Header.Get("Authorization"), "Signature=")
 			signatureValid.Store(originalSig == recomputedSig)
 		}
-		mockBedrock := newMockUpstream(ctx, t, fixResp)
+		mockBedrock := testutil.NewMockUpstream(ctx, t, fixResp)
 		mockBedrock.AllowOverflow = true
 
 		// Simulated egress proxy: modifies X-Forwarded-For and
@@ -666,7 +666,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 			defer resp.Body.Close()
 			_, _ = io.ReadAll(resp.Body)
 
-			received := mockBedrock.receivedRequests()
+			received := mockBedrock.ReceivedRequests()
 			require.NotEmpty(t, received)
 			last := received[len(received)-1]
 
@@ -716,7 +716,7 @@ func TestOpenAIChatCompletions(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, fixtures.OaiChatSingleBuiltinTool)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -794,7 +794,7 @@ func TestOpenAIChatCompletions(t *testing.T) {
 				// Setup mock server for multi-turn interaction.
 				// First request → tool call response, second → tool response.
 				fix := fixtures.Parse(t, tc.fixture)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix), newFixtureToolResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix), testutil.NewFixtureToolResponse(fix))
 
 				// Setup MCP proxies with the tool from the fixture
 				mockMCP := setupMCPForTest(t, defaultTracer)
@@ -996,7 +996,7 @@ func TestSimple(t *testing.T) {
 					t.Cleanup(cancel)
 
 					fix := fixtures.Parse(t, tc.fixture)
-					upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+					upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 					bridgeServer := newBridgeTestServer(ctx, t, upstream.URL+tc.basePath)
 
@@ -1009,7 +1009,7 @@ func TestSimple(t *testing.T) {
 					require.Equal(t, http.StatusOK, resp.StatusCode)
 
 					// Then: I expect the upstream request to have the correct path.
-					received := upstream.receivedRequests()
+					received := upstream.ReceivedRequests()
 					require.Len(t, received, 1)
 					require.Equal(t, tc.expectedPath, received[0].Path)
 
@@ -1113,7 +1113,7 @@ func TestSessionIDTracking(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL, withProvider(config.ProviderAnthropic))
 
 			reqBody := fix.Request()
@@ -1198,7 +1198,7 @@ func TestFallthrough(t *testing.T) {
 			t.Parallel()
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(t.Context(), t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(t.Context(), t, testutil.NewFixtureResponse(fix))
 			bridgeServer := newBridgeTestServer(t.Context(), t, upstream.URL+tc.basePath)
 
 			resp, err := bridgeServer.makeRequest(t, http.MethodGet, tc.requestPath, nil)
@@ -1209,7 +1209,7 @@ func TestFallthrough(t *testing.T) {
 
 			// Verify upstream received the request at the expected path
 			// with the API key header.
-			received := upstream.receivedRequests()
+			received := upstream.ReceivedRequests()
 			require.Len(t, received, 1)
 			require.Equal(t, tc.expectedUpstreamPath, received[0].Path)
 			require.Contains(t, received[0].Header.Get(tc.expectAuthHeader), apiKey)
@@ -1538,7 +1538,7 @@ func TestErrorHandling(t *testing.T) {
 						// Setup mock server. Error fixtures contain raw HTTP
 						// responses that may cause the bridge to retry.
 						fix := fixtures.Parse(t, tc.fixture)
-						upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+						upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 						bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -1610,7 +1610,7 @@ func TestErrorHandling(t *testing.T) {
 
 				// Setup mock server.
 				fix := fixtures.Parse(t, tc.fixture)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 				upstream.StatusCode = http.StatusInternalServerError
 
 				bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
@@ -1664,11 +1664,11 @@ func TestStableRequestEncoding(t *testing.T) {
 
 			// Create a mock upstream that serves the same blocking response for each request.
 			count := 10
-			responses := make([]upstreamResponse, count)
+			responses := make([]testutil.UpstreamResponse, count)
 			for i := range count {
-				responses[i] = newFixtureResponse(fix)
+				responses[i] = testutil.NewFixtureResponse(fix)
 			}
-			upstream := newMockUpstream(ctx, t, responses...)
+			upstream := testutil.NewMockUpstream(ctx, t, responses...)
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
 				withMCP(mockMCP),
@@ -1683,7 +1683,7 @@ func TestStableRequestEncoding(t *testing.T) {
 			}
 
 			// All upstream request bodies should be identical.
-			received := upstream.receivedRequests()
+			received := upstream.ReceivedRequests()
 			require.Len(t, received, count)
 			reference := string(received[0].Body)
 			for _, r := range received[1:] {
@@ -1931,7 +1931,7 @@ func TestAnthropicToolChoiceParallelDisabled(t *testing.T) {
 			}
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
 				withMCP(mockMCP),
@@ -1947,7 +1947,7 @@ func TestAnthropicToolChoiceParallelDisabled(t *testing.T) {
 			require.Equal(t, http.StatusOK, resp.StatusCode)
 
 			// Verify tool_choice in the upstream request.
-			received := upstream.receivedRequests()
+			received := upstream.ReceivedRequests()
 			require.Len(t, received, 1)
 			var receivedRequest map[string]any
 			require.NoError(t, json.Unmarshal(received[0].Body, &receivedRequest))
@@ -2087,7 +2087,7 @@ func TestChatCompletionsParallelToolCallsDisabled(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, tc.fixture)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				var opts []bridgeOption
 				if tc.withInjectedTools {
@@ -2112,7 +2112,7 @@ func TestChatCompletionsParallelToolCallsDisabled(t *testing.T) {
 				_, err = io.ReadAll(resp.Body)
 				require.NoError(t, err)
 
-				received := upstream.receivedRequests()
+				received := upstream.ReceivedRequests()
 				require.Len(t, received, 1)
 
 				var upstreamReq map[string]any
@@ -2142,7 +2142,7 @@ func TestThinkingAdaptiveIsPreserved(t *testing.T) {
 			t.Cleanup(cancel)
 
 			// Create a mock server that captures the request body sent upstream.
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -2160,7 +2160,7 @@ func TestThinkingAdaptiveIsPreserved(t *testing.T) {
 			require.NoError(t, err)
 
 			// Verify the thinking field was preserved in the upstream request.
-			received := upstream.receivedRequests()
+			received := upstream.ReceivedRequests()
 			require.Len(t, received, 1)
 			assert.Equal(t, "adaptive", gjson.GetBytes(received[0].Body, "thinking.type").Str)
 		})
@@ -2207,7 +2207,7 @@ func TestEnvironmentDoNotLeak(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			// Set environment variables that the SDK would automatically read.
 			// These should NOT leak into upstream requests.
@@ -2223,7 +2223,7 @@ func TestEnvironmentDoNotLeak(t *testing.T) {
 			require.Equal(t, http.StatusOK, resp.StatusCode)
 
 			// Verify that environment values did not leak.
-			received := upstream.receivedRequests()
+			received := upstream.ReceivedRequests()
 			require.Len(t, received, 1)
 			require.Empty(t, received[0].Header.Get(tc.headerName))
 		})
@@ -2319,7 +2319,7 @@ func TestActorHeaders(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, tc.fixture)
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				metadataKey := "Username"
 				bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
@@ -2341,7 +2341,7 @@ func TestActorHeaders(t *testing.T) {
 				_, err = io.ReadAll(resp.Body)
 				require.NoError(t, err)
 
-				received := upstream.receivedRequests()
+				received := upstream.ReceivedRequests()
 				require.NotEmpty(t, received)
 				receivedHeaders := received[0].Header
 

aibridge/internal/integrationtest/metrics_internal_test.go

@@ -147,7 +147,7 @@ func TestMetrics_Interception(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 			upstream.AllowOverflow = tc.allowOverflow
 
 			m := aibridge.NewMetrics(prometheus.NewRegistry())
@@ -256,7 +256,7 @@ func TestMetrics_PromptCount(t *testing.T) {
 	t.Cleanup(cancel)
 
 	fix := fixtures.Parse(t, fixtures.OaiChatSimple)
-	upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+	upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 	m := aibridge.NewMetrics(prometheus.NewRegistry())
 	bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
@@ -342,7 +342,7 @@ func TestMetrics_TokenUseCount(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			m := aibridge.NewMetrics(prometheus.NewRegistry())
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
@@ -383,7 +383,7 @@ func TestMetrics_NonInjectedToolUseCount(t *testing.T) {
 	t.Cleanup(cancel)
 
 	fix := fixtures.Parse(t, fixtures.OaiChatSingleBuiltinTool)
-	upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+	upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 	m := aibridge.NewMetrics(prometheus.NewRegistry())
 	bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
@@ -410,7 +410,7 @@ func TestMetrics_InjectedToolUseCount(t *testing.T) {
 
 	// First request returns the tool invocation, the second returns the mocked response to the tool result.
 	fix := fixtures.Parse(t, fixtures.AntSingleInjectedTool)
-	upstream := newMockUpstream(ctx, t, newFixtureResponse(fix), newFixtureToolResponse(fix))
+	upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix), testutil.NewFixtureToolResponse(fix))
 
 	m := aibridge.NewMetrics(prometheus.NewRegistry())
 

aibridge/internal/integrationtest/responses_internal_test.go

@@ -328,7 +328,7 @@ func TestResponsesOutputMatchesUpstream(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 
@@ -544,7 +544,7 @@ func TestResponsesParallelToolsOverwritten(t *testing.T) {
 				t.Cleanup(cancel)
 
 				fix := fixtures.Parse(t, tc.fixture[i])
-				upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+				upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 				var opts []bridgeOption
 				if tc.withInjectedTools {
@@ -567,7 +567,7 @@ func TestResponsesParallelToolsOverwritten(t *testing.T) {
 				_, err = io.ReadAll(resp.Body)
 				require.NoError(t, err)
 
-				received := upstream.receivedRequests()
+				received := upstream.ReceivedRequests()
 				require.Len(t, received, 1)
 
 				var upstreamReq map[string]any
@@ -873,7 +873,7 @@ func TestResponsesInjectedTool(t *testing.T) {
 			// Setup mock server for multi-turn interaction.
 			// First request → tool call response, second → tool response.
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix), newFixtureToolResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix), testutil.NewFixtureToolResponse(fix))
 
 			// Setup MCP server proxies (with mock tools).
 			mockMCP := setupMCPForTest(t, defaultTracer)
@@ -1023,7 +1023,7 @@ func TestResponsesModelThoughts(t *testing.T) {
 			t.Cleanup(cancel)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL)
 

aibridge/internal/integrationtest/setupbridge.go

@@ -216,10 +216,10 @@ func setupInjectedToolTest(
 	// Setup mock server for multi-turn interaction.
 	// First request → tool call response
 	// Second request → final response.
-	firstResp := newFixtureResponse(fix)
-	toolResp := newFixtureToolResponse(fix)
+	firstResp := testutil.NewFixtureResponse(fix)
+	toolResp := testutil.NewFixtureToolResponse(fix)
 	toolResp.OnRequest = toolRequestValidatorFn
-	upstream := newMockUpstream(ctx, t, firstResp, toolResp)
+	upstream := testutil.NewMockUpstream(ctx, t, firstResp, toolResp)
 
 	mockMCP := setupMCPForTest(t, tracer)
 

aibridge/internal/integrationtest/trace_internal_test.go

@@ -147,7 +147,7 @@ func TestTraceAnthropic(t *testing.T) {
 			sr, tracer := setupTracer(t)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			opts := []bridgeOption{
 				withTracer(tracer),
@@ -263,7 +263,7 @@ func TestTraceAnthropicErr(t *testing.T) {
 			sr, tracer := setupTracer(t)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 
 			opts := []bridgeOption{
 				withTracer(tracer),
@@ -552,7 +552,7 @@ func TestTraceOpenAI(t *testing.T) {
 			sr, tracer := setupTracer(t)
 
 			fix := fixtures.Parse(t, tc.fixture)
-			upstream := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 			bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
 				withTracer(tracer),
 			)
@@ -711,7 +711,7 @@ func TestTraceOpenAIErr(t *testing.T) {
 
 			fix := fixtures.Parse(t, tc.fixture)
 
-			mockAPI := newMockUpstream(ctx, t, newFixtureResponse(fix))
+			mockAPI := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
 			mockAPI.AllowOverflow = tc.allowOverflow
 			bridgeServer := newBridgeTestServer(ctx, t, mockAPI.URL,
 				withTracer(tracer),
@@ -753,7 +753,7 @@ func TestTracePassthrough(t *testing.T) {
 
 	fix := fixtures.Parse(t, fixtures.OaiChatFallthrough)
 
-	upstream := newMockUpstream(t.Context(), t, newFixtureResponse(fix))
+	upstream := testutil.NewMockUpstream(t.Context(), t, testutil.NewFixtureResponse(fix))
 
 	sr, tracer := setupTracer(t)
 

aibridge/internal/testutil/mockserverproxier.go

@@ -0,0 +1,47 @@
+package testutil
+
+import (
+	"context"
+
+	mcpgo "github.com/mark3labs/mcp-go/mcp"
+
+	"github.com/coder/coder/v2/aibridge/mcp"
+)
+
+// MockServerProxier is a test [mcp.ServerProxier] that injects a fixed set of
+// tools.
+type MockServerProxier struct {
+	Tools []*mcp.Tool
+}
+
+func (*MockServerProxier) Init(context.Context) error {
+	return nil
+}
+
+func (*MockServerProxier) Shutdown(context.Context) error {
+	return nil
+}
+
+func (m *MockServerProxier) ListTools() []*mcp.Tool {
+	return m.Tools
+}
+
+func (m *MockServerProxier) GetTool(id string) *mcp.Tool {
+	for _, t := range m.Tools {
+		if t.ID == id {
+			return t
+		}
+	}
+	return nil
+}
+
+func (*MockServerProxier) CallTool(context.Context, string, any) (*mcpgo.CallToolResult, error) {
+	return nil, nil //nolint:nilnil // mock: no-op implementation
+}
+
+// StubToolCaller is a minimal tool client that returns a fixed text result.
+type StubToolCaller struct{}
+
+func (StubToolCaller) CallTool(_ context.Context, _ mcpgo.CallToolRequest) (*mcpgo.CallToolResult, error) {
+	return mcpgo.NewToolResultText("tool result"), nil
+}

aibridge/internal/testutil/mockupstream.go

@@ -1,4 +1,4 @@
-package integrationtest
+package testutil
 
 import (
 	"bufio"
@@ -25,10 +25,10 @@ import (
 	"github.com/coder/coder/v2/aibridge/intercept/eventstream"
 )
 
-// upstreamResponse defines a single response that mockUpstream will replay
-// for one incoming request. Use [newFixtureResponse] or [newFixtureToolResponse] to
+// UpstreamResponse defines a single response that MockUpstream will replay
+// for one incoming request. Use [NewFixtureResponse] or [NewFixtureToolResponse] to
 // construct one from a parsed txtar archive.
-type upstreamResponse struct {
+type UpstreamResponse struct {
 	Streaming []byte // returned when the request has "stream": true.
 	Blocking  []byte // returned for non-streaming requests.
 
@@ -37,11 +37,11 @@ type upstreamResponse struct {
 	OnRequest func(r *http.Request, body []byte)
 }
 
-// newFixtureResponse creates an upstreamResponse from a parsed fixture archive.
+// NewFixtureResponse creates an UpstreamResponse from a parsed fixture archive.
 // It reads whichever of 'streaming' and 'non-streaming' sections exist;
 // not every fixture has both (e.g. error fixtures may only define one).
-func newFixtureResponse(fix fixtures.Fixture) upstreamResponse {
-	var resp upstreamResponse
+func NewFixtureResponse(fix fixtures.Fixture) UpstreamResponse {
+	var resp UpstreamResponse
 	if fix.Has(fixtures.SectionStreaming) {
 		resp.Streaming = fix.Streaming()
 	}
@@ -51,11 +51,11 @@ func newFixtureResponse(fix fixtures.Fixture) upstreamResponse {
 	return resp
 }
 
-// newFixtureToolResponse creates an upstreamResponse from the tool-call fixture files.
+// NewFixtureToolResponse creates an UpstreamResponse from the tool-call fixture files.
 // It reads whichever of 'streaming/tool-call' and 'non-streaming/tool-call'
 // sections exist.
-func newFixtureToolResponse(fix fixtures.Fixture) upstreamResponse {
-	var resp upstreamResponse
+func NewFixtureToolResponse(fix fixtures.Fixture) UpstreamResponse {
+	var resp UpstreamResponse
 	if fix.Has(fixtures.SectionStreamingToolCall) {
 		resp.Streaming = fix.StreamingToolCall()
 	}
@@ -65,31 +65,36 @@ func newFixtureToolResponse(fix fixtures.Fixture) upstreamResponse {
 	return resp
 }
 
-// newErrorResponse returns an upstreamResponse that replays a raw HTTP error
-// response with the given status code. Used to drive iteration-N error paths
-// from inside a multi-call mockUpstream scripted-response list.
-func newErrorResponse(status int) upstreamResponse {
+// NewErrorResponse returns an UpstreamResponse that replays a raw HTTP error
+// response with the given status code and optional Retry-After header. SDK
+// auto-retries are disabled via x-should-retry.
+func NewErrorResponse(status int, retryAfter string) UpstreamResponse {
 	body := fmt.Sprintf(`{"error":{"message":%q}}`, http.StatusText(status))
+
 	raw := fmt.Sprintf("HTTP/1.1 %d %s\r\n", status, http.StatusText(status))
+	if retryAfter != "" {
+		raw += fmt.Sprintf("Retry-After: %s\r\n", retryAfter)
+	}
 	raw += "x-should-retry: false\r\n"
 	raw += "Content-Type: application/json\r\n"
 	raw += fmt.Sprintf("Content-Length: %d\r\n\r\n%s", len(body), body)
+
 	rawBytes := []byte(raw)
-	return upstreamResponse{Streaming: rawBytes, Blocking: rawBytes}
+	return UpstreamResponse{Streaming: rawBytes, Blocking: rawBytes}
 }
 
-// receivedRequest captures the details of a single request handled by mockUpstream.
-type receivedRequest struct {
+// ReceivedRequest captures the details of a single request handled by MockUpstream.
+type ReceivedRequest struct {
 	Method string
 	Path   string
 	Header http.Header
 	Body   []byte
 }
 
-// mockUpstream replays txtar fixture responses, validates incoming request
+// MockUpstream replays txtar fixture responses, validates incoming request
 // bodies, and counts calls. It stands in for a real AI provider API
 // (Anthropic, OpenAI) during integration tests.
-type mockUpstream struct {
+type MockUpstream struct {
 	*httptest.Server
 
 	// Calls is incremented atomically on every request.
@@ -107,31 +112,31 @@ type mockUpstream struct {
 	AllowOverflow bool
 
 	mu       sync.Mutex
-	requests []receivedRequest
+	requests []ReceivedRequest
 
 	t         *testing.T
-	responses []upstreamResponse
+	responses []UpstreamResponse
 }
 
-// receivedRequests returns a copy of all requests received so far.
-func (ms *mockUpstream) receivedRequests() []receivedRequest {
+// ReceivedRequests returns a copy of all requests received so far.
+func (ms *MockUpstream) ReceivedRequests() []ReceivedRequest {
 	ms.mu.Lock()
 	defer ms.mu.Unlock()
-	return append([]receivedRequest(nil), ms.requests...)
+	return append([]ReceivedRequest(nil), ms.requests...)
 }
 
-// newMockUpstream creates a started httptest.Server that replays fixture
+// NewMockUpstream creates a started httptest.Server that replays fixture
 // responses. Responses are returned in order: first call → first response.
 // The test fails if the number of requests doesn't match the number of
 // responses (when AllowOverflow is not set, default).
 //
-//	srv := newMockUpstream(ctx, t, newFixtureResponse(fix))                        // simple
-//	srv := newMockUpstream(ctx, t, newFixtureResponse(fix), newFixtureToolResponse(fix)) // multi-turn
-func newMockUpstream(ctx context.Context, t *testing.T, responses ...upstreamResponse) *mockUpstream {
+//	srv := NewMockUpstream(ctx, t, NewFixtureResponse(fix))                        // simple
+//	srv := NewMockUpstream(ctx, t, NewFixtureResponse(fix), NewFixtureToolResponse(fix)) // multi-turn
+func NewMockUpstream(ctx context.Context, t *testing.T, responses ...UpstreamResponse) *MockUpstream {
 	t.Helper()
-	require.NotEmpty(t, responses, "at least one upstreamResponse required")
+	require.NotEmpty(t, responses, "at least one UpstreamResponse required")
 
-	ms := &mockUpstream{
+	ms := &MockUpstream{
 		t:         t,
 		responses: responses,
 	}
@@ -156,7 +161,7 @@ func newMockUpstream(ctx context.Context, t *testing.T, responses ...upstreamRes
 	return ms
 }
 
-func (ms *mockUpstream) handle(w http.ResponseWriter, r *http.Request) {
+func (ms *MockUpstream) handle(w http.ResponseWriter, r *http.Request) {
 	call := int(ms.Calls.Add(1) - 1)
 
 	body, err := io.ReadAll(r.Body)
@@ -164,7 +169,7 @@ func (ms *mockUpstream) handle(w http.ResponseWriter, r *http.Request) {
 	require.NoError(ms.t, err)
 
 	ms.mu.Lock()
-	ms.requests = append(ms.requests, receivedRequest{
+	ms.requests = append(ms.requests, ReceivedRequest{
 		Method: r.Method,
 		Path:   r.URL.Path,
 		Header: r.Header.Clone(),
@@ -201,7 +206,7 @@ func (ms *mockUpstream) handle(w http.ResponseWriter, r *http.Request) {
 	_, _ = w.Write(resp.Blocking)
 }
 
-func (ms *mockUpstream) responseForCall(call int) upstreamResponse {
+func (ms *MockUpstream) responseForCall(call int) UpstreamResponse {
 	if call >= len(ms.responses) {
 		if ms.AllowOverflow {
 			return ms.responses[len(ms.responses)-1]
@@ -218,7 +223,7 @@ func isStreaming(body []byte, urlPath string) bool {
 	return gjson.GetBytes(body, "stream").Bool() || strings.HasSuffix(urlPath, "invoke-with-response-stream")
 }
 
-func (ms *mockUpstream) writeSSE(w http.ResponseWriter, data []byte) {
+func (ms *MockUpstream) writeSSE(w http.ResponseWriter, data []byte) {
 	ms.t.Helper()
 
 	w.Header().Set("Content-Type", "text/event-stream")
@@ -257,7 +262,7 @@ func isRawHTTPResponse(data []byte) bool {
 // writeRawHTTPResponse parses data as a complete HTTP response and replays it,
 // copying the status code, headers, and body to w. This supports error fixtures
 // that contain full HTTP responses (e.g. "HTTP/2.0 400 Bad Request\r\n...").
-func (ms *mockUpstream) writeRawHTTPResponse(w http.ResponseWriter, r *http.Request, data []byte) {
+func (ms *MockUpstream) writeRawHTTPResponse(w http.ResponseWriter, r *http.Request, data []byte) {
 	ms.t.Helper()
 
 	resp, err := http.ReadResponse(bufio.NewReader(bytes.NewReader(data)), r)