TDD Example

This example goes through the entire process of TDD (Red-Green-Refactor) for writing an Add macro

1. Stub out the Add method with the desired signature (input and output types), but leave the method body blank. (You want to set up the tests before writing any code)

   Function Add(A As Double, B As Double) As Double
   
   End Function

2. Add initial specs for the method

   Public Function Specs() As SpecSuite
       ' Create a new collection of specs
       Set Specs = New SpecSuite
       Specs.Description = "Add"
   
       ' Report results to Immediate Window
       ' (ctrl + g or View > Immediate Window)
       Dim Reporter As New ImmediateReporter
       Reporter.ListenTo Specs
   
       ' Describe the desired behavior
       With Specs.It("should add 2 numbers")
           ' Test the desired behavior
           .Expect(Add(2, 2)).ToEqual 4
           .Expect(Add(3, -1)).ToEqual 2
           .Expect(Add(-1, -2)).ToEqual -3
       End With
   End Function

3. (Red) Open the immediate window (Ctrl+g or View > Immediate Window) and run the specs (F5) before writing the Add method to verify that the tests are currently failing (running properly since no code has been written yet)

   ' === Add ===
   ' X should add 2 numbers
   '   Expected 0 to equal 4
   '   Expected 0 to equal 2
   '   Expected 0 to equal -3
   ' = FAIL (1 of 1 failed) =
   ' Failure is a good thing! It means our tests are working since we haven't written Add yet

4. (Green) Write just enough in the Add method for the specs to pass and then re-run the specs (F5)

   Function Add(A As Double, B As Double) As Double
       Add = A + B
   End Function
   
   ' === Add ===
   ' + should add 2 numbers
   ' = PASS (1 of 1 passed) =
   ' Success!

5. (Refactor) Let's say you wanted to expand the Add method to allow for any number of arguments. Start with a refactor of the currently tested behavior.

   Function Add(ParamArray Values() As Variant) As Double
       Add = Values(0) + Values(1)
   End Function
   
   ' === Add ===
   ' + should add 2 numbers
   ' = PASS (1 of 1 passed) =
   ' Good!

6. Then add specs for the desired new behavior that will fail initially

   Public Function Specs() As SpecSuite
       Set Specs = New SpecSuite
       Specs.Description = "Add"
   
       Dim Reporter As New ImmediateReporter
       Reporter.ListenTo Specs
   
       With Specs.It("should add 2 numbers")
           ' Test the desired behavior
           .Expect(Add(2, 2)).ToEqual 4
           .Expect(Add(3, -1)).ToEqual 2
           .Expect(Add(-1, -2)).ToEqual -3
       End With
   
       With Specs.It("should add any number of numbers")
           .Expect(Add(1, 2, 3)).ToEqual 6
           .Expect(Add(1, 2, 3, 4)).ToEqual 10
       End With
   End Function
   
   ' === Add ===
   ' + should add 2 numbers
   ' X should add any number of numbers
   '   Expected 3 to equal 6
   '   Expected 3 to equal 10
   ' = FAIL (1 of 2 failed) =
   ' Failure is ok, we haven't written this functionality yet

7. Then work on Add until all of the specs pass

   Public Function Add(ParamArray Values() As Variant) As Double
       Dim i As Integer
       Add = 0
       
       For i = LBound(Values) To UBound(Values)
           Add = Add + Values(i)
       Next i
   End Function
   
   ' === Add ===
   ' + should add 2 numbers
   ' + should add any number of numbers
   ' = PASS (2 of 2 passed) =
   ' Woohoo!