Code Coverage Incorrect for Parameter Default When Using New Profiler

[wethreetrees]

General summary of the issue

When using the new code coverage profiler ($PesterPreference.CodeCoverage.UseBreakpoints = $false), Pester is reporting missing commands for parameter default value expressions.

ex:

[Int]$Temperature = (Get-Random -Maximum 100 -Minimum 0)

This is working, as expected, when using breakpoints ($PesterPreference.CodeCoverage.UseBreakpoints = $true)

Describe your environment

Pester version : 5.3.1 C:\Client\PowerShell\Modules\Pester\5.3.1\Pester.psm1
PowerShell version : 7.2.1
OS version : Microsoft Windows NT 10.0.19042.0

Steps to reproduce

1. Download and extract the PesterCCProfilerIssue.zip
2. From the target directory, run:

.\Invoke-Tests.ps1

Expected Behavior

Should return no missing commands with 100% code coverage.

Current Behavior

Returns:

Covered 75% / 75%. 4 analyzed Commands in 1 File.
 Missed command:
 
File            Class Function        Line Command
----            ----- --------        ---- -------
TestModule.psm1       Get-Temperature    6 Get-Random -Maximum 100 -Minimum 0

Possible Solution? (optional)

😕

[fflaten]

Thanks for the report. I can confirm the issue.

The following lines might indicate it's a known limitation because we couldn't register a hit for parameter values either way.

Pester/src/functions/Coverage.ps1

Lines 1213 to 1218 in 13d6595

	if ($last -is [System.Management.Automation.Language.ParamBlockAst]) {
	# param block will not indicate that any of the default values in it executed,
	# and the block itself is not reported by the tracer. So we will land here with the parame block as the $last
	# and we need to take the containing scriptblock (be it actual scriptblock, or a function definition), which is the parent
	# of this param block.
	$last = $parent

CC debug of Get-Temperature (notice that the param block isn't hit).

PS /workspaces/Pester/Samples/PesterCCProfilerIssue> 
DBG: 9+     end  >>>> {
EXP: /workspaces/Pester/Samples/PesterCCProfilerIssue/TestModule.psm1:9:9:{
DBG: 10+         if ( >>>> $Temperature -gt 50) {
EXP: /workspaces/Pester/Samples/PesterCCProfilerIssue/TestModule.psm1:10:13:$Temperature -gt 50
DBG: 13+         return  >>>> 'Thats Cold'
EXP: /workspaces/Pester/Samples/PesterCCProfilerIssue/TestModule.psm1:13:16:'Thats Cold'
DBG: 14+      >>>> }
EXP: /workspaces/Pester/Samples/PesterCCProfilerIssue/TestModule.psm1:14:5:}

However if I use Set-PSDebug -Trace 1 (the same events the profiler hooks into) it shows line 6 being called when default parameter value is used:

> Get-Temperature -Temperature 1
DEBUG:    1+  >>>> Get-Temperature -Temperature 1
DEBUG:    9+     end  >>>> {
DEBUG:   10+         if ( >>>> $Temperature -gt 50) {
DEBUG:   13+         return  >>>> 'Thats Cold'
Thats Cold
DEBUG:   14+      >>>> }

> Get-Temperature
DEBUG:    1+  >>>> Get-Temperature
** DEBUG:    6+         [Int]$Temperature =  >>>> (Get-Random -Maximum 100 -Minimum 0) **
DEBUG:    9+     end  >>>> {**
DEBUG:   10+         if ( >>>> $Temperature -gt 50) {
DEBUG:   13+         return  >>>> 'Thats Cold'
Thats Cold
DEBUG:   14+      >>>> }

@nohwnd, do you remember any of this? If powershell traces line 6, shouldn't we get it too? Are we excluding it for some reason?

[fflaten]

Oh, I see it. The message show the parameter value being calculated, but the extent we're able to get at that point is just the reference/call to the function.

[nohwnd]

Yeah I think this was one of the limitations, there is a test that compares old cc with new, and comments on what we can do better than the previous CC and what we can do worse. This is probably one of the (few) things we do worse.

https://github.com/pester/Pester/blob/main/tst/CoverageTestFile.ps1
https://github.com/pester/Pester/blob/main/tst/Pester.RSpec.Coverage.ts.ps1#L30