Add test for default value with optional input

lib/galaxy_test/workflow/default_values_optional.gxwf-tests.yml

@@ -0,0 +1,34 @@
+- doc: |
+    Test that default value doesn't need to be supplied
+  job: {}
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "1"
+- doc: |
+    Test that null is replaced with default value (follows https://www.commonwl.org/v1.2/Workflow.html#WorkflowInputParameter)
+  job:
+    optional_int_with_default:
+      type: raw
+      value: null
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "1"
+- doc: |
+    Test that empty string is not replaced and fails
+  expect_failure: true
+  job:
+    optional_int_with_default:
+      type: raw
+      value: ""
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "1"

lib/galaxy_test/workflow/default_values_optional.gxwf.yml

@@ -0,0 +1,18 @@
+class: GalaxyWorkflow
+inputs:
+  optional_int_with_default:
+    type: int
+    default: 1
+    optional: true
+outputs:
+  out:
+    outputSource: integer_default/out_file1
+steps:
+  integer_default:
+    tool_id: integer_default
+    tool_state:
+      input1: 0
+      input2: 0
+    in:
+      input3:
+        source: optional_int_with_default