public void ValidateInput_Function_Test() { var calculator = new Calculator1(); Assert.AreEqual(-1, calculator.ValidateInput_Function("three")); Assert.AreEqual(-1, calculator.ValidateInput_Function("87654")); Assert.AreEqual(11, calculator.ValidateInput_Function("11")); Assert.AreEqual(-1, calculator.ValidateInput_Function("0")); Assert.AreEqual(-1, calculator.ValidateInput_Function("1.5")); }