Why does JUnit assertEquals( -0.0, 0.0 ) fail?

user_1319809 0
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I'm working with JUnit 5 in Java SE 11 and discovered that assertEquals(-0.0,0.0) fails. Why is that? Java itself is perfectly happy with "-0. == 0.". Sample code follows.

double  dVar1   = 0;
double  dVar2   = -dVar1;
System.out.println( dVar1 == dVar2 ); // true
System.out.println( -0. == 0. );      // true
assertEquals( dVar1, dVar2, .00001 ); // passes
assertEquals( 0.0, -0.0, .0001 );     // passes
assertEquals( 0.0, -0.0 );            // fails
assertEquals( dVar1, dVar2 );         // fails
junit java
1 Answers

Java has no problem with -0 and 0. But in assertEquals method use this method from Double class to convert params to longBits and the reterned values are not the same.

 public static long doubleToLongBits(double value) {
        long result = doubleToRawLongBits(value);
        // Check for NaN based on values of bit fields, maximum
        // exponent and nonzero significand.
        if ( ((result & DoubleConsts.EXP_BIT_MASK) ==
              DoubleConsts.EXP_BIT_MASK) &&
             (result & DoubleConsts.SIGNIF_BIT_MASK) != 0L)
            result = 0x7ff8000000000000L;
        return result;
    }

In your case you have to use the first assertEquals(double expected, double actual, double delta) which based on math operation: return doublesAreEqual(value1, value2) || Math.abs(value1 - value2) <= delta

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