TDD Example

Testing 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

   Sub Specs()
       ' Create a new collection of specs
       On Error Resume Next
       Dim Specs As New SpecSuite
   
       ' Describe the desired behavior
       With Specs.It("should add two 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
   
       ' Run the specs inline (in the Immediate window)
       InlineRunner.RunSuite Specs
   End Sub

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)

   = FAIL (1 of 1 failed) ==========================
   X should add 2 numbers
     Expected 0 to equal 4
     Expected 0 to equal 2
     Expected 0 to equal -3
   ===
   ' 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
   
   = 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
   
   = PASS (1 of 1 passed) ==========================
   ' Success!

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

   Sub Specs()
       On Error Resume Next
       Dim Specs As New SpecSuite
   
       With Specs.It("should add two numbers")
           .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
   
       InlineRunner.RunSuite Specs
   End Sub
   
   = FAIL (1 of 2 failed) ==========================
   X should add any number of numbers
     Expected 3 to equal 6
     Expected 3 to equal 10
   ===
   ' 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
   
   = PASS (2 of 2 passed) ==========================
   ' Woohoo!