C# / Visual Studio Unit Test AreEqual failes even though it is correct [duplicate]

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• Is floating point math broken? 28 answers

I am currently discovering Visual Studio's Unix Tests and wrote a little Test Project for it. It is a simple Console Calculator with the following two methods:

public static double divide(double zahl1, double zahl2)
    {
        return zahl1 / zahl2;
    }

    public static double add(double zahl1, double zahl2)
    {
        return zahl1 + zahl2;
    }

I automatically created the Unix Tests for those two methods. Then entered the Testing Code:

public void divideTest()
    {
        double zahl1 = 6.6;
        double zahl2 = 8.8;
        double result = 0.0;
        double expected = 0.75;

        result = Taschenrechner.divide(zahl1, zahl2);
        Assert.AreEqual(expected, result);
    }

    [TestMethod()]
    public void addTest()
    {
        double zahl1 = 10.5;
        double zahl2 = 5.4;
        double result = 0.0;
        double expected = 15.9;

        result = Taschenrechner.add(zahl1, zahl2);
        Assert.AreEqual(expected, result);
    }

If I now run those tests, addTest() works fine, but divideTest() fails:

Error Message

Funny thing being that it says Expected: 0.75, Actual: 0.75 which should be right.

What am I doing wrong?

Edit: I may also add that the addTest() takes <1ms while divideTest() takes 131ms.