Google Testing Blog: January 2017

Testing on the Toilet: Keep Cause and Effect Clear

Tuesday, January 31, 2017

by Ben Yu

This article was adapted from a Google Testing on the Toilet (TotT) episode. You can download a printer-friendly version of this TotT episode and post it in your office. Can you tell if this test is correct? 208: @Test public void testIncrement_existingKey() { 209: assertEquals(9, tally.get("key1")); 210: }It’s impossible to knowtally1: private final Tally tally = new Tally(); 2: @Before public void setUp() { 3: tally.increment("key1", 8); 4: tally.increment("key2", 100); 5: tally.increment("key1", 0); 6: tally.increment("key1", 1); 7: } // 200 lines away 208: @Test public void testIncrement_existingKey() { 209: assertEquals(9, tally.get("key1")); 210: }key1occurs 200+ lines away from the assertionthe cause is hidden far away from the effectwrite tests where the effects immediately follow the causescauseeffect1: private final Tally tally = new Tally(); 2: @Test public void testIncrement_newKey() { 3: tally.increment("key", 100); 5: assertEquals(100, tally.get("key")); 6: } 7: @Test public void testIncrement_existingKey() { 8: tally.increment("key", 8); 9: tally.increment("key", 1); 10: assertEquals(9, tally.get("key")); 11: } 12: @Test public void testIncrement_incrementByZeroDoesNothing() { 13: tally.increment("key", 8); 14: tally.increment("key", 0); 15: assertEquals(8, tally.get("key")); 16: }The payback is in more readable code and lower maintenance costs.