Added unit tests for Addition, Subtraction, Multiplication, and Equal To Operators

TestOpAddition  [PASS]
TestOpAdditionAssignment  [PASS]  
TestOpSubtraction  [PASS]
TestOpSubtractionAssignment  [PASS]
TestOpMultiplication  [PASS]
TestOpMultiplicationAssignment  [PASS]
TestOpEqualTo  [PASS]

@dnesbitt61 @gknisely @kevinkreiser