Fix Abs unit test (#260)

***NO_CI***

(cherry picked from commit a809347)

Author: josesimoes

Tests/MathUnitTests/MathUnitTest.cs

@@ -228,12 +228,12 @@ public static void Test_Abs_double()
             double answer = 0.0029832;
             double res = Math.Abs(val);
 
-            Assert.NotEqual(res, answer, "Abs(...double val - negative) -- FAILED AT: {res}");
+            Assert.AreEqual(res, answer, $"Abs(...double val - negative) -- FAILED AT: {res}");
 
             val = 0.0029832;
             answer = 0.0029832;
             res = Math.Abs(val);
-            Assert.NotEqual(res, answer, "Abs(...double val - positive) -- FAILED AT: {res}");
+            Assert.AreEqual(res, answer, $"Abs(...double val - positive) -- FAILED AT: {res}");
 
         }