Is there any way to test functions in a PowerShell script without executing the script? - powershell

Question

I would like to define stand-alone functions in my PowerShell script and be able to Pester test the functions without executing the rest of the script. Is there any way to do this without defining the functions in a separate file?
In the following pseudocode example, how do I test functionA or functionB without executing mainFunctionality?
script.ps1:
functionA
functionB
...
mainFunctionality
script.Tests.ps1:
BeforeAll {
. $PSScriptRoot/script.ps1 # This will execute the mainFunctionality, which is what I want to avoid
}
Describe 'functionA' {
# ... tests
}
I believe in Python, you can do this by wrapping your "mainFunctionality" inside this condition, so I am looking for something similar in Powershell.
if __name__ == '__main__':
mainFunctionality
Ref: What does if __name__ == "__main__": do?

Answer 1

Using the PowerShell Abstract Syntax Tree (AST) to just grab functionA and invoke it:
$ScriptBlock = {
function functionA {
Write-Host 'Do something A'
}
function functionB {
Write-Host 'Do something A'
}
function mainFunctionality {
# Do something
functionA
# Do something
functionB
# Do something
}
mainFunctionality
}
Using NameSpace System.Management.Automation.Language
$Ast = [Parser]::ParseInput($ScriptBlock, [ref]$null, [ref]$null) # or: ParseFile
$FunctionA = $Ast.FindAll({
$Args[0] -is [ScriptBlockAst] -and $Args[0].Parent.Name -eq 'functionA'
}, $True)
Invoke-Expression $FunctionA.EndBlock
Do something A

Answer 2

You could use $MyInvocation.PSCommandPath to determine who invoked your script, its the closest I can think of to Python's if __name__ == '__main__':. This property will give you the absolute path of the caller. From there you can extract the script name, i.e. with Path.GetFileName and after you can determine what you want to do, for example, call mainFunctionality if the caller's name equals to main.ps1 or call mainFunctionality if the caller's name is not equal to script.Tests.ps1.
Here is a short example.
myScript.ps1
function A {
"I'm function A"
}
function B {
"I'm function B"
}
function mainFunctionality {
"I'm function mainFunctionality"
}
A # Calls A
B # Calls B
# Call `mainFunctionality` only if my caller's name is `main.ps1`
if([System.IO.Path]::GetFileName($MyInvocation.PSCommandPath) -eq 'main.ps1') {
mainFunctionality
}
Then if calling myScript.ps1 from main.ps1 you would see:
I'm function A
I'm function B
I'm function mainFunctionality
And if calling myScript.ps1 from anywhere else (console or other script with a different name) you would see:
I'm function A
I'm function B

Answer 3

Yes, you can use the Invoke-Expression cmdlet to test functions in a PowerShell script without executing the script. This cmdlet allows you to execute a string as if it were a command.
For example, if you have a function called Test-Function in your script, you can use the following command to test it: Invoke-Expression -Command "Test-Function"
function functionA {
# Do something
}
function functionB {
# Do something
}
function mainFunctionality {
# Do something
functionA
# Do something
functionB
# Do something
}
mainFunctionality
Yes, you can test functions in a PowerShell script without executing the rest of the script. To do this, you can use the Invoke-Pester command to run specific tests in the script. For example, if you wanted to test the functions functionA and functionB, you could use the following command:
Invoke-Pester -Script .\MyScript.ps1 -TestName functionA,functionB
This will execute the tests for the specified functions without executing the rest of the script.