Java By Comparison

Use Reasonable Tolerance Values

class OxygenTankTest {

    @Test
    void testNewTankIsEmpty() {
        OxygenTank tank = OxygenTank.withCapacity(100);
        Assertions.assertEquals(0, tank.getStatus());
    }

    @Test
    void testFilling() {
        OxygenTank tank = OxygenTank.withCapacity(100);

        tank.fill(5.8);
        tank.fill(5.6);

        Assertions.assertEquals(0.114, tank.getStatus());
    }
}

Here you can see tests that use floating-point numbers instead of integer values. From the source code alone, the tests seem good. The problem is that they’re going to fail, even if the code that’s tested is functionally correct.

Can you think of why? Here’s a tip: On our machine, the second test fails with the message expected: <0.114> but was <0.11399999999999999> ...