Add some simple tests to sanity check the time machine gc.

test/test_gc.py

@@ -1,4 +1,5 @@
 import unittest
+import time
 
 from app import app, storage
 from initdb import setup_database_for_testing, finished_database_for_testing
@@ -210,5 +211,34 @@ class TestGarbageColection(unittest.TestCase):
     self.gcNow(repository)
     self.assertNotDeleted(repository, 'i1', 'i2', 'i3', 't1', 't2', 't3', 'f1', 'f2')
 
+  def test_time_machine_no_gc(self):
+    """ Repository has two tags with shared images. Deleting the tag should not remove any images
+    """
+    repository = self.createRepository(latest=['i1', 'i2', 'i3'], other=['i1', 'f1'])
+    self._set_tag_expiration_policy(repository.namespace_user.username, 60*60*24)
+
+    self.deleteTag(repository, 'latest')
+    self.assertNotDeleted(repository, 'i2', 'i3')
+    self.assertNotDeleted(repository, 'i1', 'f1')
+
+  def test_time_machine_gc(self):
+    """ Repository has two tags with shared images. Deleting the second tag should cause the images
+        for the first deleted tag to gc.
+    """
+    repository = self.createRepository(latest=['i1', 'i2', 'i3'], other=['i1', 'f1'])
+
+    self._set_tag_expiration_policy(repository.namespace_user.username, 1)
+
+    self.deleteTag(repository, 'latest')
+    self.assertNotDeleted(repository, 'i2', 'i3')
+    self.assertNotDeleted(repository, 'i1', 'f1')
+
+    time.sleep(2)
+
+    self.deleteTag(repository, 'other')  # This will cause the images associated with latest to gc
+    self.assertDeleted(repository, 'i2', 'i3')
+    self.assertNotDeleted(repository, 'i1', 'f1')
+
+
 if __name__ == '__main__':
   unittest.main()