Test that TensorFlow is not imported on startup (#904)

* test tf not imported on startup

* add require_tf

* better comment

* Update test_import.py

* add pytest ./tests/test_tf*

.github/workflows/python-tests.yml

@@ -95,6 +95,8 @@ jobs:
         pip install --upgrade pip
         pip install .[testing,tensorflow]
 
+    - run: pytest --cov -Werror::FutureWarning -sv ./tests/test_tf*
+
     - run: pytest --cov -Werror::FutureWarning -sv ./tests/test_keras*
 
     - name: Upload coverage reports to Codecov with GitHub Action

tests/test_tf_import.py

@@ -0,0 +1,26 @@
+import sys
+import unittest
+
+from huggingface_hub.file_download import is_tf_available
+
+
+def require_tf(test_case):
+    """
+    Decorator marking a test that requires TensorFlow.
+
+    These tests are skipped when TensorFlow is not installed.
+
+    """
+    if not is_tf_available():
+        return unittest.skip("test requires Tensorflow")(test_case)
+    else:
+        return test_case
+
+
+@require_tf
+def test_import_huggingface_hub_doesnt_import_tensorfow():
+    # `import huggingface_hub` is not necessary since huggingface_hub is already imported at the top of this file,
+    # but let's keep it here anyway just in case
+    import huggingface_hub  # noqa
+
+    assert "tensorflow" not in sys.modules