Excel VBA: In a loop, why am I losing my active workbook when I evaluate another sub? - vba

Question

I am modifying a function for looping through all workbooks in a folder and performing an action on each.
In the code below, if I un-comment the Module1.TestSub line, the loop performs TestSub on each file in the chosen folder, as expected.
But I want it to work as a function, taking another sub or function as it's argument and performing that on the loop, so that I could run LoopThroughWorkbooks (Module1.TestSub) and not have to edit LoopThroughWorkbooks every time I want to loop a different action.
If I instead un-comment the Evaluate (myAction) line, it seems to still loop through the intended files doing nothing, and performs Module1.TestSub on the file I had active to begin with.
It seems like the Evaluate (myAction) line is losing track of the workbook opened by the loop in a way that doesn't happen when I just explicitly call Module1.TestSub.
Function LoopThroughWorkbooks(myAction As String)
'PURPOSE: To loop through all xls* files in a user specified folder and perform an action
'SOURCE: www.TheSpreadsheetGuru.com
Dim wb As Workbook
Dim myPath As String
Dim myFile As String
Dim myExtension As String
Dim FldrPicker As FileDialog
'Optimize Macro Speed
Application.ScreenUpdating = False
Application.EnableEvents = False
Application.Calculation = xlCalculationManual
'Retrieve Target Folder Path From User
Set FldrPicker = Application.FileDialog(msoFileDialogFolderPicker)
With FldrPicker
.Title = "Select A Target Folder"
.AllowMultiSelect = False
If .Show <> -1 Then GoTo NextCode
myPath = .SelectedItems(1) & "\"
End With
'In Case of Cancel
NextCode:
myPath = myPath
If myPath = "" Then GoTo ResetSettings
'Target File Extension (must include wildcard "*")
myExtension = "*.xls*"
'Target Path with Ending Extention
myFile = Dir(myPath & myExtension)
'Loop through each Excel file in folder
Do While myFile <> ""
'Set variable equal to opened workbook
Set wb = Workbooks.Open(Filename:=myPath & myFile)
'Ensure Workbook has opened before moving on to next line of code
DoEvents
'Do Action Specified in Argument
'Module1.TestSub <<<<<<<<<<<<<<<< This line works
'Evaluate (myAction) <<<<<<<<<<<<<<<< This line doesn't
'Save and Close Workbook
wb.Close SaveChanges:=True
'Ensure Workbook has closed before moving on to next line of code
DoEvents
'Get next file name
myFile = Dir
Loop
'Message Box when tasks are completed
MsgBox "Looping Complete!"
'Reset Macro Optimization Settings
ResetSettings:
Application.EnableEvents = True
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True
End Function
And in case it's helpful, here's Module1.TestSub:
Function TestSub()
Range("A1") = "AAA"
End Function
And here's how I'm calling it:
Sub runtest()
Module2.LoopThroughWorkbooks (Module1.TestSub)
End Sub