openapi3: update tests for OAS 3.1 field gate

Three tests need adjustment now that OAS 3.1-only schema fields are
rejected under OAS 3.0 validation:

- TestSchemaIfThenElse_Validate and TestSchemaValidate31SubSchemas
  exercise 3.1 features (If/Then/Else, PrefixItems) directly via
  Schema.Validate without a doc, so the isOpenAPI31OrLater flag is
  never set from a doc version. Pass IsOpenAPI31OrLater() explicitly.

- TestIssue495WithDraft04{,Bis} load OAS 3.0 documents that $ref
  external JSON Schema draft-04 meta-schemas (which contain $id and
  $schema). Add AllowExtraSiblingFields("$id", "$schema") so the
  tests assertion about the unresolved inner "#" ref surfaces as
  intended, matching the pattern already used in issue513_test.go.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

Author: reuvenharrison

openapi3/issue495_test.go

@@ -121,7 +121,10 @@ paths:
 	doc, err := sl.LoadFromData(spec)
 	require.NoError(t, err)
 
-	err = doc.Validate(sl.Context)
+	// draft-04 meta-schema contains $id and $schema; in OAS 3.0 these require
+	// opt-in via AllowExtraSiblingFields so the test can assert its real target
+	// (the unresolved inner "#" ref).
+	err = doc.Validate(sl.Context, AllowExtraSiblingFields("$id", "$schema"))
 	require.ErrorContains(t, err, `found unresolved ref: "#"`)
 }
 
@@ -157,6 +160,9 @@ paths:
 	doc, err := sl.LoadFromData(spec)
 	require.NoError(t, err)
 
-	err = doc.Validate(sl.Context)
+	// draft-04 meta-schema contains $id and $schema; in OAS 3.0 these require
+	// opt-in via AllowExtraSiblingFields so the test can assert its real target
+	// (the unresolved inner "#" ref).
+	err = doc.Validate(sl.Context, AllowExtraSiblingFields("$id", "$schema"))
 	require.ErrorContains(t, err, `found unresolved ref: "#"`)
 }

openapi3/schema_if_then_else_test.go

@@ -176,7 +176,7 @@ func TestSchemaIfThenElse_Validate(t *testing.T) {
 		schema := &openapi3.Schema{
 			If: &openapi3.SchemaRef{Ref: "#/components/schemas/Missing"},
 		}
-		err := schema.Validate(context.Background())
+		err := schema.Validate(context.Background(), openapi3.IsOpenAPI31OrLater())
 		require.Error(t, err)
 		require.ErrorContains(t, err, "unresolved ref")
 	})
@@ -185,7 +185,7 @@ func TestSchemaIfThenElse_Validate(t *testing.T) {
 		schema := &openapi3.Schema{
 			Then: &openapi3.SchemaRef{Ref: "#/components/schemas/Missing"},
 		}
-		err := schema.Validate(context.Background())
+		err := schema.Validate(context.Background(), openapi3.IsOpenAPI31OrLater())
 		require.Error(t, err)
 		require.ErrorContains(t, err, "unresolved ref")
 	})
@@ -194,7 +194,7 @@ func TestSchemaIfThenElse_Validate(t *testing.T) {
 		schema := &openapi3.Schema{
 			Else: &openapi3.SchemaRef{Ref: "#/components/schemas/Missing"},
 		}
-		err := schema.Validate(context.Background())
+		err := schema.Validate(context.Background(), openapi3.IsOpenAPI31OrLater())
 		require.Error(t, err)
 		require.ErrorContains(t, err, "unresolved ref")
 	})
@@ -205,7 +205,7 @@ func TestSchemaIfThenElse_Validate(t *testing.T) {
 			Then: &openapi3.SchemaRef{Value: &openapi3.Schema{MinLength: 1}},
 			Else: &openapi3.SchemaRef{Value: &openapi3.Schema{Type: &openapi3.Types{"number"}}},
 		}
-		err := schema.Validate(context.Background())
+		err := schema.Validate(context.Background(), openapi3.IsOpenAPI31OrLater())
 		require.NoError(t, err)
 	})
 }

openapi3/schema_validate_31_test.go

@@ -9,7 +9,7 @@ import (
 )
 
 func TestSchemaValidate31SubSchemas(t *testing.T) {
-	ctx := context.Background()
+	ctx := openapi3.WithValidationOptions(context.Background(), openapi3.IsOpenAPI31OrLater())
 
 	// Helper: a schema with an invalid nested schema (pattern with bad regex)
 	invalidSchema := &openapi3.Schema{