when(commit.getTimestamp()).thenReturn(new Date(42));
TestModel testModelA = new TestModel("A", 42);
TestModel testModelB = new TestModel("B", -42);
engine.execute(new InsertOperation(commit, testIndex, new ArrayList(Arrays.asList(testModelA, testModelB))));
IndexCommit deleteCommit = mock(IndexCommit.class);
when(deleteCommit.getTimestamp()).thenReturn(new Date(84));
engine.execute(new DeleteOperation(deleteCommit, testIndex, new ArrayList(Arrays.asList(testModelB))));