Handle the case when the failure message contains an escape sequence

[JamesWTruher]

…which may occur with PowerShell 7

1. General summary of the pull request

If the failure message contains an escape sequence (which can happen with PowerShell 7, and the results are going to be serialized to an Nunit file, you may see something like this:

MethodInvocationException: /Users/jimtru/src/github/forks/JamesWTruher/Pester/Functions/TestResults.ps1
Line |
 591 |             $xmlWriter.WriteElementString('message', $TestResult.FailureMessage)
     |             ^ Exception calling "WriteElementString" with "2" argument(s): "', hexadecimal value 0x1B, is an invalid character."

and the xml file created is partial. The escape in the message is not valid for serialization

This escapes the escape character ([char]27) to &27;

[nohwnd]

@JamesWTruher not 100% sure how to repro the error with escapes on my PowerShell 7, please verify the changes.

The cast to string here is unnecessary, but I kept it anyway to keep it same as in the code file. (There it is needed to force use of Replace(string, string) instead of Replace(char, char) which fails.

[JamesWTruher]

i'll grant you that my test is quite artificial, but here's the way to see it:

PS> Get-Content /tmp/t1.tests.ps1
describe "a simple test" {
    it "can handle an error with an escape sequence" {
       throw  "`e[31m < < , > > `e[0m"
    }
}

when run as follows, you can see the error:

[Pester|master↑0↓0•0+0?0] PS> invoke-pester /tmp/t1.tests.ps1 -OutputFile /tmp/xx.xml -OutputFormat NUnitXml
    ____            __
   / __ \___  _____/ /____  _____
  / /_/ / _ \/ ___/ __/ _ \/ ___/
 / ____/  __(__  ) /_/  __/ /
/_/    \___/____/\__/\___/_/
Pester v4.9.0
Executing all tests in '/tmp/t1.tests.ps1'

Executing script /tmp/t1.tests.ps1

  Describing a simple test
    [-] can handle an error with an escape sequence 1ms
      RuntimeException:  < < , > > 
      at <ScriptBlock>, /tmp/t1.tests.ps1: line 3
Tests completed in 24ms
Tests Passed: 0, Failed: 1, Skipped: 0, Pending: 0, Inconclusive: 0 
MethodInvocationException: /Users/jimtru/src/github/forks/JamesWTruher/Pester/Functions/TestResults.ps1
Line |
 591 |             $xmlWriter.WriteElementString('message', $TestResult.FailureMessage)
     |             ^ Exception calling "WriteElementString" with "2" argument(s): "', hexadecimal value 0x1B, is an invalid character."

[JamesWTruher]

@nohwnd - I probably should have put that in the test, but it seemed like too much.