Add tests for caching.

tests/collection_test.py

@@ -0,0 +1,59 @@
+"""Tests for the fex FeatureExtractor Collection."""
+
+import os
+import tempfile
+import unittest
+
+import fex
+import test_classes as tc
+
+
+class CallCounterMock(object):
+    """Mocking class to count function calls.
+
+    Python mock library cannot be used because cannot be pickled for caching.
+    """
+
+    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 = tc.TestExtractor('1', 'col_1', 42)
+        test_extractor.extract = CallCounterMock()
+        collection = fex.Collection(self.cache_file)
+        collection.add_feature_extractor(test_extractor)
+        collection.run(self.dataset_file)
+        self.assertEqual(test_extractor.extract.counter, 1)
+        collection = fex.Collection(self.cache_file)
+        collection.add_feature_extractor(test_extractor)
+        collection.run(self.dataset_file)
+        self.assertEqual(test_extractor.extract.counter, 1)
+        collection = fex.Collection(self.cache_file)
+        collection.add_feature_extractor(test_extractor)
+        test_extractor._source_hash = 'new_value'
+        collection.run(self.dataset_file)
+        self.assertEqual(test_extractor.extract.counter, 2)
+
+if __name__ == '__main__':
+    unittest.main()  # pragma: no cover