public void FindByVariableName_ThrowsArgumentExceptionIfThereIsNoMembershipFunctionForVariable()
        {
            // Arrange
            string variableName = "FunctionNr4";

            // Act & Assert
            Assert.Throws <ArgumentException>(() => { _membershipFunctionList.FindByVariableName(variableName); });
        }
        public void FindByVariableName_ThrowsArgumentNullExceptionIfThereAreNoMembershipFunctionsInList()
        {
            // Arrange
            _membershipFunctionList = new MembershipFunctionList();
            string variableName = "AnyName";

            // Act & Assert
            Assert.Throws <ArgumentNullException>(() => { _membershipFunctionList.FindByVariableName(variableName); });
        }