visual studio 2012 - Actual And Expected values are same but unit test fails. Why? -

i trying learn unit test on vs 2012 , tried this:

 public class calculator  {     public double substraction(double num1, double num2)     {         return num1 - num2;     }  } 

and test class here:

[testclass] public class unittest1 {     [testmethod]     public void calc_substract()     {         var calculator = new calculator();         assert.areequal<double>(calculator.substraction(5.3, 1.1), 4.2);     } } 

gives error:

test name:  calc_substract test fullname:  myunittest.unittest1.calc_substract test source:    d:\users\... test outcome:   failed test duration:  0:00:00,0068363  **result message:   assert.areequal failed. expected:<4,2>. actual:<4,2>.** 

as see, values same test fails. know why?

very odd, i'm wondering if it's loss of precision issue since you're working doubles - although values seem innocuous enough not trigger precision issues.

also, fantastic result message :).

does @ least pass if ask compare 4.2 4.2:

assert.areequal<double>(4.2, 4.2); 

?

would curious see happens if plug in rounding:

assert.areequal<double>(math.round(calculator.substraction(5.3, 1.1),1), 4.2); 

also, consider using decimal instead of double has greater precision , more naturally represents exact decimals, should find precision issues cases specific test avoided decimal - although that's not other, more complex cases, won't still suffer precision issues decimal