public void ChangeLeftOperandSign_ChangesRighOperandSignCorrectly(string rightOperand, string expectedValue)
{
// Arrange
var calculatorModel = new CalculatorModel();
calculatorModel.RightOperand = rightOperand;
// Act
calculatorModel.ChangeRightOperandSign();
// Assert
Assert.AreEqual(expectedValue, calculatorModel.RightOperand);
}
