Add tests for caching.

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tests/collection_test.py

@@ -0,0 +1,56 @@
+"""Tests for the fex FeatureExtractor Collection."""
+
+import os
+import tempfile
+import unittest
+
+import fex
+import mock_extractor as me
+
+
+# Python mock library cannot be used because cannot be pickled for caching.
+class _CallCounterMock(object):
+    """Mocking class to count function calls."""
+
+    def __init__(self):
+        """Set counter to zero."""
+        super(_CallCounterMock, self).__init__()
+        self.counter = 0
+
+    def __call__(self):
+        """Record calls to class instances."""
+        self.counter = self.counter + 1
+
+
+class CollectionTest(unittest.TestCase):
+    """Test feature extractor collection."""
+
+    def setUp(self):
+        """Create temporary file and test data."""
+        self.dataset_file = tempfile.mktemp()
+        self.cache_file = tempfile.mktemp()
+
+    def tearDown(self):
+        """Remove the file after the test."""
+        os.remove(self.dataset_file)
+        os.remove(self.cache_file)
+
+    def test_extract_should_not_be_called_if_hash_unchanged(self):
+        """Feature extractor should only be re-computed when source changed."""
+        test_extractor = me.MockExtractor('1', 'col_1', 42)
+        test_extractor.extract = _CallCounterMock()
+
+        # Create collection, add extractor and run (extract should be called).
+        collection = fex.Collection(self.cache_file)
+        collection.add_feature_extractor(test_extractor)
+        collection.run(self.dataset_file)
+        counter_first_run = test_extractor.extract.counter
+
+        # Create a new collection with same extractor and run.
+        collection2 = fex.Collection(self.cache_file)
+        collection2.add_feature_extractor(test_extractor)
+        collection2.run(self.dataset_file)
+        self.assertEqual(counter_first_run, test_extractor.extract.counter)
+
+if __name__ == '__main__':
+    unittest.main()  # pragma: no cover