| Both JUnit and Truth allow for asserting equality of floating point numbers with |
| an absolute tolerance. For example, the following statements are equivalent, |
| |
| ```java |
| double EPSILON = 1e-20; |
| assertThat(actualValue).isWithin(EPSILON).of(Math.PI); |
| assertEquals(Math.PI, actualValue, EPSILON); |
| ``` |
| |
| What's not immediately obvious is that both of these assertions are checking |
| exact equality between `Math.PI` and `actualValue`, because the next `double` |
| after `Math.PI` is `Math.PI + 4.44e-16`. |
| |
| This means that using the same tolerance to compare several floating point |
| values with different magnitude can be prone to error, |
| |
| ```java |
| float TOLERANCE = 1e-5f; |
| assertThat(pressure).isWithin(TOLERANCE).of(1f); // GOOD |
| assertThat(pressure).isWithin(TOLERANCE).of(10f); // GOOD |
| assertThat(pressure).isWithin(TOLERANCE).of(100f); // BAD -- misleading equals check |
| ``` |
| |
| A larger tolerance should be used if the goal of the test is to allow for some |
| floating point errors, or, if not, `isEqualTo` makes the intention more clear. |
