I changed what you suggested and I still cant get the tests to go through, look at the test results:

Test Results:
Fixed tests
Tests
should return 1 litre: '1' should equal 1
Test Passed
should return 6 litres: '6' should equal 6
Test Passed
should return 5 litres: '5' should equal 5
should return 893 litres: '893' should equal 893
Test Passed

inexplicable lol.