Generating tests dynamically for each model

dbt_bouncer/runner.py

@@ -1,3 +1,4 @@
+import inspect
 from typing import Dict, List
 
 import pytest
@@ -22,6 +23,41 @@ def tests(self):
         return self.tests_
 
 
+# Inspiration: https://github.com/pytest-dev/pytest-xdist/discussions/957#discussioncomment-7335007
+class MyFunctionItem(pytest.Function):
+    def __init__(self, model, *args, **kwargs):
+        self.model: Dict[str, str] = model
+        super().__init__(*args, **kwargs)
+
+
+class GenerateTestsPlugin:
+    """
+    For fixtures that are lists (e.g. `models`) this plugin generates a test for each item in the list.
+    Using alternaticve approaches like parametrize or fixture_params do not work, generating tests using
+    `pytest_pycollect_makeitem` is one way to get this to work.
+    """
+
+    def __init__(self, models):
+        self.models = models
+
+    def pytest_pycollect_makeitem(self, collector, name, obj):
+        items = []
+        if (inspect.isfunction(obj) or inspect.ismethod(obj)) and (name.startswith("test_")):
+            fixture_info = pytest.Function.from_parent(
+                collector, name=name, callobj=obj
+            )._fixtureinfo
+            for model in self.models:
+                item = MyFunctionItem.from_parent(
+                    parent=collector,
+                    name=name,
+                    fixtureinfo=fixture_info,
+                    model=model,
+                )
+                items.append(item)
+
+        return items
+
+
 def runner(
     models: List[Dict[str, str]],
     sources: List[Dict[str, str]],
@@ -37,4 +73,7 @@ def runner(
         setattr(fixtures, att + "_", locals()[att])
 
     # Run the tests, if one fails then pytest will raise an exception
-    pytest.main(["dbt_bouncer/tests"], plugins=[fixtures])
+    pytest.main(
+        ["dbt_bouncer/tests"],
+        plugins=[fixtures, GenerateTestsPlugin(models)],
+    )

dbt_bouncer/tests/test_models.py

@@ -1,13 +1,9 @@
-def populated_model_description(models):
+def test_populated_model_description(request, model=None):
     """
     Models must have a populated description.
     """
 
-    for model in models:
-        assert (
-            len(model["description"].strip()) > 4
-        ), f"{model['unique_id']} does not have a populated description."
-
-
-def test_populated_model_description(models):
-    populated_model_description(models=models)
+    model = request.node.model if model is None else model
+    assert (
+        len(model["description"].strip()) > 4
+    ), f"{model['unique_id']} does not have a populated description."

tests/conftest.py

@@ -0,0 +1,21 @@
+import importlib
+from pathlib import Path
+
+
+def pytest_collection_modifyitems(session, config, items):
+    """
+    Pytest runs all functions that start with "test_". This is an issue as out functions in
+    `./dbt_bouncer/tests` also have this prefix and therefore pytest tries to test those.
+    This hook is used to dynamically retrieve the names of these functions and remove them
+    from the list of functions that pytest will run.
+    """
+
+    dbt_bouncer_tests: list[str] = []
+    for f in Path("./dbt_bouncer/tests").glob("**/*"):
+        if f.is_file() and f.name.startswith("test_") and f.name.endswith(".py"):
+            test_file = importlib.import_module(f"dbt_bouncer.tests.{f.stem}")
+            dbt_bouncer_tests.extend(
+                i for i in dir(test_file) if not i.startswith("_") and i != "logger"
+            )
+
+    items[:] = [item for item in items if item.name not in dbt_bouncer_tests]

tests/tests/test_models.py

@@ -2,81 +2,67 @@
 
 import pytest
 
-from dbt_bouncer.tests.test_models import populated_model_description
+from dbt_bouncer.tests.test_models import test_populated_model_description
 
 
 @pytest.mark.parametrize(
-    "models,expectation",
+    "model, expectation",
     [
         (
-            [
-                {
-                    "description": "Description that is more than 4 characters.",
-                    "unique_id": "model.package_name.model_1",
-                }
-            ],
+            {
+                "description": "Description that is more than 4 characters.",
+                "unique_id": "model.package_name.model_1",
+            },
             does_not_raise(),
         ),
         (
-            [
-                {
-                    "description": """A
+            {
+                "description": """A
                         multiline
                         description
                         """,
-                    "unique_id": "model.package_name.model_2",
-                }
-            ],
+                "unique_id": "model.package_name.model_2",
+            },
             does_not_raise(),
         ),
         (
-            [
-                {
-                    "description": "",
-                    "unique_id": "model.package_name.model_3",
-                }
-            ],
+            {
+                "description": "",
+                "unique_id": "model.package_name.model_3",
+            },
             pytest.raises(AssertionError),
         ),
         (
-            [
-                {
-                    "description": " ",
-                    "unique_id": "model.package_name.model_4",
-                }
-            ],
+            {
+                "description": " ",
+                "unique_id": "model.package_name.model_4",
+            },
             pytest.raises(AssertionError),
         ),
         (
-            [
-                {
-                    "description": """
+            {
+                "description": """
                         """,
-                    "unique_id": "model.package_name.model_5",
-                }
-            ],
+                "unique_id": "model.package_name.model_5",
+            },
             pytest.raises(AssertionError),
         ),
         (
-            [
-                {
-                    "description": "-",
-                    "unique_id": "model.package_name.model_6",
-                }
-            ],
+            {
+                "description": "-",
+                "unique_id": "model.package_name.model_6",
+            },
             pytest.raises(AssertionError),
         ),
         (
-            [
-                {
-                    "description": "null",
-                    "unique_id": "model.package_name.model_7",
-                }
-            ],
+            {
+                "description": "null",
+                "unique_id": "model.package_name.model_7",
+            },
             pytest.raises(AssertionError),
         ),
     ],
 )
-def test_populated_model_description(models, expectation):
+def test_test_populated_model_description(model, expectation):
     with expectation:
-        populated_model_description(models=models)
+        test_populated_model_description(model=model, request=None)