Junit assert double arrays

Question

How do I assert that two arrays of double s contain the same elements. There are methods to assert that arrays of integers and other primitive types contain the same elements but not for double s.

Answer 1

JUnit 4.12 has (actually it is already part of 4.6, the oldest version available at github)

org.junit.Assert.assertArrayEquals(double[] expecteds, double[] actuals, double delta)
org.junit.Assert.assertArrayEquals(String message, ddouble[] expecteds, double[] actuals, double delta)

See https://github.com/junit-team/junit4/blob/r4.12/src/main/java/org/junit/Assert.java , source line 482 and 498

Answer 2

If you are not using a version of JUnit that supports double array comparison then the simplest solution would be to use Arrays.equals :

assertTrue(Arrays.equals(array1, array2));

However this won't cope with rounding errors in the way the Junit double asserts do.

Answer 3

Normally you compare doubles with a tolerance for the rounding errors. A solution to this problem using Java 8 and JUnit 5:

  public static final double TOLERANCE = 1e-9;

  @ParameterizedTest
  @MethodSource("getValues")
  public void testArrayOfDoublesEquals(double a, double b)
  {
    assertEquals(a, b, TOLERANCE);
  }

  private static Stream<Arguments> getValues() {
    double[] arrayA = new double[] {1.0, 2.097, 3.98000000001};
    double[] arrayB = new double[] {1.0, 2.097, 3.98000000000};

    List<Arguments> args = new ArrayList<>();
    for(int i = 0; i < arrayA.length; i++) {      
      args.add(Arguments.of(arrayA[i], arrayB[i]));
    }
    return args.stream();
  }

Better than assertArrayEquals because you can visualize the test result element by element: