Add test

tests/test_openapi_custom_schema_generator.py

@@ -0,0 +1,81 @@
+import pytest
+from fastapi import FastAPI
+from fastapi._compat import PYDANTIC_V2, GenerateJsonSchema
+from fastapi.openapi.utils import get_openapi
+
+app = FastAPI()
+
+
+@app.get("/")
+def read_root():
+    pass  # pragma: no cover
+
+
+# Custom schema generator that does nothing but tracks if it was called
+class CustomJsonSchemaGenerator(GenerateJsonSchema):
+    def __init__(self):
+        super().__init__()
+        self.called = False
+
+    def generate_definitions(self, *args, **kwargs):
+        self.called = True
+        return super().generate_definitions(*args, **kwargs)
+
+
+def test_custom_schema_generator_called():
+    custom_schema_generator = CustomJsonSchemaGenerator()
+    get_openapi(
+        title=app.title,
+        version=app.version,
+        routes=app.routes,
+        schema_generator=custom_schema_generator,
+    )
+
+    if PYDANTIC_V2:
+        assert custom_schema_generator.called is True
+    else:
+        assert (  # Pydantic v1 does not use custom schema generators
+            custom_schema_generator.called is False
+        )
+
+
+@pytest.mark.parametrize("use_custom_schema_generator", [True, False])
+def test_custom_schema_generator_openapi(use_custom_schema_generator: bool):
+    custom_schema_generator = (
+        CustomJsonSchemaGenerator() if use_custom_schema_generator else None
+    )
+    openapi = get_openapi(
+        title=app.title,
+        version=app.version,
+        routes=app.routes,
+        schema_generator=custom_schema_generator,
+    )
+
+    assert openapi == OPENAPI_SCHEMA
+
+
+OPENAPI_SCHEMA = {
+    "info": {
+        "title": "FastAPI",
+        "version": "0.1.0",
+    },
+    "openapi": "3.1.0",
+    "paths": {
+        "/": {
+            "get": {
+                "operationId": "read_root__get",
+                "responses": {
+                    "200": {
+                        "content": {
+                            "application/json": {
+                                "schema": {},
+                            },
+                        },
+                        "description": "Successful Response",
+                    },
+                },
+                "summary": "Read Root",
+            },
+        },
+    },
+}