This fuzzy equality check is using a tolerance less than the gap to the next number. You may want a less restrictive tolerance, or to assert equality.


The problem

Both JUnit and Truth allow for asserting equality of floating point numbers with an absolute tolerance. For example, the following statements are equivalent,

double EPSILON = 1e-20;
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,

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.


Suppress false positives by adding the suppression annotation @SuppressWarnings("FloatingPointAssertionWithinEpsilon") to the enclosing element.