fixed pandas backports tests

Author: daniel-sanche

tests/unit/test_pandas_backports.py

@@ -12,25 +12,46 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import builtins
 import unittest.mock as mock
 
 import db_dtypes.pandas_backports as pandas_backports
 
+REAL_IMPORT = builtins.__import__
+
+
+def _import_side_effect(module_name, result_return=None, result_raise=None):
+    """
+    Builds a side-effect for mocking the import function. 
+    If the imported package matches `name`, it will return or raise based on
+    arguments. Otherwise, it will default to regular import behaviour
+    """
+    def _impl(name, *args, **kwargs):
+        if name == module_name:
+            if result_raise:
+                raise result_raise
+            else:
+                return result_return
+        else:
+            return REAL_IMPORT(name, *args, **kwargs)
+    return _impl
+
 
 @mock.patch("builtins.__import__")
 def test_import_default_module_found(mock_import):
     mock_module = mock.MagicMock()
-    mock_module.OpsMixin = "OpsMixin_from_module"  # Simulate successful import
-    mock_import.return_value = mock_module
+    mock_module.OpsMixin = "OpsMixin_from_module"
+
+    mock_import.side_effect = _import_side_effect("module_name", mock_module)
 
     default_class = type("OpsMixin", (), {})  # Dummy class
     result = pandas_backports.import_default("module_name", default=default_class)
     assert result == "OpsMixin_from_module"
 
 
 @mock.patch("builtins.__import__")
-def test_import_default_module_not_found(mock_import):
-    mock_import.side_effect = ModuleNotFoundError
+def test_import_default_module_not_foundX(mock_import):
+    mock_import.side_effect = _import_side_effect("module_name", result_raise=ModuleNotFoundError)
 
     default_class = type("OpsMixin", (), {})  # Dummy class
     result = pandas_backports.import_default("module_name", default=default_class)
@@ -48,6 +69,7 @@ def test_import_default_force_true(mock_import):
     result = pandas_backports.import_default(
         "any_module_name", force=True, default=default_class
     )
+    assert mock_import.call_count == 0
 
     # Assert that the returned value is the default class itself
     assert result is default_class