Add marker for TF tests (#272)

**Description of the Change:**

- Tests using the soft requirement tensorflow needs to be marked
`@pytest.mark.tf`.
- It also unlocks only running those tests (or not) `pytest -m tf
tests/` `pytest -m not tf tests/`
- If TF is not installed the tests are skipped.

conftest.py → frontend/test/pytest/conftest.py

@@ -1,6 +1,29 @@
-"""Setup pytest configurations."""
+# Copyright 2023 Xanadu Quantum Technologies Inc.
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Pytest configuration file for Catalyst test suite.
+"""
+# pylint: disable=unused-import
 import pytest
 
+try:
+    import tensorflow as tf
+except (ImportError, ModuleNotFoundError) as e:
+    tf_available = False
+else:
+    tf_available = True
+
 
 def pytest_addoption(parser):
     """Add pytest custom options."""
@@ -42,6 +65,31 @@ def pytest_configure(config):
     )
 
 
+def pytest_runtest_setup(item):
+    """Automatically skip tests if interfaces are not installed"""
+    interfaces = {"tf"}
+    available_interfaces = {
+        "tf": tf_available,
+    }
+
+    allowed_interfaces = [
+        allowed_interface
+        for allowed_interface in interfaces
+        if available_interfaces[allowed_interface] is True
+    ]
+
+    # load the marker specifying what the interface is
+    all_interfaces = {"tf"}
+    marks = {mark.name for mark in item.iter_markers() if mark.name in all_interfaces}
+
+    for b in marks:
+        if b not in allowed_interfaces:
+            pytest.skip(
+                f"\nTest {item.nodeid} only runs with {allowed_interfaces}"
+                f" interfaces(s) but {b} interface provided",
+            )
+
+
 def pytest_collection_modifyitems(config, items):
     """A pytest items modifier method"""
 

frontend/test/pytest/pytest.ini

@@ -0,0 +1,3 @@
+[pytest]
+markers =
+    tf: marks tests for tf testing (select with '-m "tf"')

frontend/test/pytest/test_autograph.py

@@ -14,7 +14,6 @@
 
 """PyTests for the AutoGraph source-to-source transformation feature."""
 
-import os
 
 import numpy as np
 import pennylane as qml
@@ -27,18 +26,20 @@
 # pylint: disable=unnecessary-lambda-assignment
 
 
-class TestIntegration:
-    """Test that the autograph transformations trigger correctly in different settings."""
+def test_unavailable(mocker):
+    """Check the error produced in the absence of tensorflow."""
+    mocker.patch.dict("sys.modules", {"tensorflow": None})
 
-    def test_unavailable(self, monkeypatch):
-        """Check the error produced in the absence of tensorflow."""
-        monkeypatch.syspath_prepend(os.path.join(os.path.dirname(__file__), "mock"))
+    def fn(x):
+        return x**2
 
-        def fn(x):
-            return x**2
+    with pytest.raises(ImportError, match="AutoGraph feature in Catalyst requires TensorFlow"):
+        qjit(autograph=True)(fn)
 
-        with pytest.raises(ImportError, match="AutoGraph feature in Catalyst requires TensorFlow"):
-            qjit(autograph=True)(fn)
+
+@pytest.mark.tf
+class TestIntegration:
+    """Test that the autograph transformations trigger correctly in different settings."""
 
     def test_unsupported_object(self):
         """Check the error produced when attempting to convert an unsupported object (neither of
@@ -188,6 +189,7 @@ def fn(x: float):
         assert fn(np.pi) == -1
 
 
+@pytest.mark.tf
 class TestCodePrinting:
     """Test that the transformed source code can be printed in different settings."""
 
@@ -317,6 +319,7 @@ def fn(x: float):
         assert autograph_source(inner)
 
 
+@pytest.mark.tf
 class TestConditionals:
     """Test that the autograph transformations produce correct results on conditionals.
     These tests are adapted from the test_conditionals.TestCond class of tests."""

requirements.txt

@@ -10,6 +10,7 @@ isort
 
 lit
 pytest
+pytest-mock
 pytest-xdist
 pytest-cov
 nbmake