chore: Add testpackage linter (#156)

Enforces a consistent test package layout.
This makes it difficult to test internal
functionality, which I believe promotes
healthy decomposition, and minimal package
exports.

.golangci.yml

@@ -241,6 +241,7 @@ linters:
     - staticcheck
     - structcheck
     - tenv
+    - testpackage
     - tparallel
     - typecheck
     - unconvert

provisioner/terraform/parse_test.go

@@ -1,6 +1,6 @@
 //go:build linux
 
-package terraform
+package terraform_test
 
 import (
 	"context"
@@ -11,6 +11,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/coder/coder/provisioner/terraform"
 	"github.com/coder/coder/provisionersdk"
 	"github.com/coder/coder/provisionersdk/proto"
 )
@@ -27,7 +28,7 @@ func TestParse(t *testing.T) {
 		cancelFunc()
 	})
 	go func() {
-		err := Serve(ctx, &ServeOptions{
+		err := terraform.Serve(ctx, &terraform.ServeOptions{
 			ServeOptions: &provisionersdk.ServeOptions{
 				Listener: server,
 			},

provisioner/terraform/provision_test.go

@@ -1,6 +1,6 @@
 //go:build linux
 
-package terraform
+package terraform_test
 
 import (
 	"context"
@@ -11,6 +11,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/coder/coder/provisioner/terraform"
 	"github.com/coder/coder/provisionersdk"
 	"github.com/coder/coder/provisionersdk/proto"
 )
@@ -26,7 +27,7 @@ func TestProvision(t *testing.T) {
 		cancelFunc()
 	})
 	go func() {
-		err := Serve(ctx, &ServeOptions{
+		err := terraform.Serve(ctx, &terraform.ServeOptions{
 			ServeOptions: &provisionersdk.ServeOptions{
 				Listener: server,
 			},

site/embed_test.go

@@ -1,4 +1,4 @@
-package site
+package site_test
 
 import (
 	"context"
@@ -8,12 +8,14 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/site"
 )
 
 func TestIndexPageRenders(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(Handler())
+	srv := httptest.NewServer(site.Handler())
 
 	req, err := http.NewRequestWithContext(context.Background(), "GET", srv.URL, nil)
 	require.NoError(t, err)