diff --git a/eng/common-tests/README.md b/eng/common-tests/README.md
new file mode 100644
index 00000000000..eb487ee7978
--- /dev/null
+++ b/eng/common-tests/README.md
@@ -0,0 +1,26 @@
+# About common-tests
+
+Every PowerShell source that is complex enough to have unit tests should have these tests be written in the [Pester](https://pester.dev/)
+framework and placed in `eng/common-tests/**`, i.e. this directory or one of its descendants.  
+By design, unlike `eng/common`, `eng/common-tests` is not subject to
+[mirroring to repositories](https://github.com/Azure/azure-sdk-tools/blob/main/doc/common/common_engsys.md).
+
+## When tests in this directory are executed
+
+The PowerShell Pester unit tests will be executed by the public
+[`tools - eng-common-tests`](https://dev.azure.com/azure-sdk/public/_build?definitionId=5985&_a=summary) pipeline upon a PR that makes changes
+to `eng/common/scripts/**` or  `eng/common-tests/**`. The pipeline source is `eng/common-tests/ci.yml`.
+
+In addition, specific tools might selectively run a subset of tests during their pipeline run, as e.g. done by `tools/code-owners-parser/ci.yml`.
+
+## How to ensure your PowerShell pester unit test is executed
+
+By Pester's default convention, the tests are to be placed in files whose
+[names ends with `.tests.ps1`](https://pester.dev/docs/usage/file-placement-and-naming),
+e.g. [`job-matrix-functions.tests.ps1`](https://github.com/Azure/azure-sdk-tools/blob/8a02e02adfc0d213509fce2764132afa74bd4ba4/eng/common-tests/matrix-generator/tests/job-matrix-functions.tests.ps1).
+
+Furthermore, each test needs to be tagged with `UnitTest`, [e.g. as seen here](https://github.com/Azure/azure-sdk-tools/blob/8a02e02adfc0d213509fce2764132afa74bd4ba4/eng/common-tests/matrix-generator/tests/job-matrix-functions.tests.ps1#L51): `Describe "Matrix-Lookup" -Tag "UnitTest", "lookup"`.
+
+Finally, as already mentioned, all such test files must be located in the path of `eng/common-tests/**`.
+
+For more, see [Invoke-Pester doc](https://pester.dev/docs/commands/Invoke-Pester).
\ No newline at end of file
diff --git a/eng/common-tests/ci.yml b/eng/common-tests/ci.yml
index 3137391791f..b017ac706f5 100644
--- a/eng/common-tests/ci.yml
+++ b/eng/common-tests/ci.yml
@@ -8,8 +8,8 @@ trigger:
       - hotfix/*
   paths:
     include:
-      - eng/common/scripts/*
-      - eng/common-tests/*
+      - eng/common/scripts
+      - eng/common-tests
 
 pr:
   branches:
@@ -20,11 +20,11 @@ pr:
       - hotfix/*
   paths:
     include:
-      - eng/common/scripts/*
-      - eng/common-tests/*
+      - eng/common/scripts
+      - eng/common-tests
 
 extends:
   template: /eng/common/pipelines/templates/stages/archetype-sdk-tool-pwsh.yml
   parameters:
-    TargetDirectory: eng/common-tests/
-    TargetTags: 'UnitTest'
+    TargetDirectory: eng/common-tests
+    TargetTags: UnitTest
diff --git a/eng/common-tests/get-codeowners/get-codeowners.tests.ps1 b/eng/common-tests/get-codeowners/get-codeowners.tests.ps1
new file mode 100644
index 00000000000..8ec82832fee
--- /dev/null
+++ b/eng/common-tests/get-codeowners/get-codeowners.tests.ps1
@@ -0,0 +1,46 @@
+Import-Module Pester
+
+BeforeAll {
+  . $PSScriptRoot/../../common/scripts/get-codeowners.lib.ps1
+
+    function TestGetCodeowners(
+      [string] $TargetPath, 
+      [string] $CodeownersFileLocation, 
+      [string[]] $ExpectedOwners
+    ) 
+    {
+      Write-Host "Test: Owners for path '$TargetPath' in CODEOWNERS file at path '$CodeownersFileLocation' should be '$ExpectedOwners'"
+      
+      $actualOwners = Get-Codeowners `
+        -TargetPath $TargetPath `
+        -CodeownersFileLocation $CodeownersFileLocation `
+    
+      $actualOwners.Count | Should -Be $ExpectedOwners.Count
+      for ($i = 0; $i -lt $ExpectedOwners.Count; $i++) {
+        $ExpectedOwners[$i] | Should -Be $actualOwners[$i]
+      }
+    }
+}
+
+Describe "Get Codeowners" -Tag "UnitTest" {
+    It "Should get Codeowners" -TestCases @(
+      @{
+        # The $PSScriptRoot is assumed to be azure-sdk-tools/eng/common-tests/get-codeowners/get-codeowners.tests.ps1
+        codeownersPath = "$PSScriptRoot/../../../.github/CODEOWNERS"; 
+        targetPath = "eng/common/scripts/get-codeowners/get-codeowners.ps1"; 
+        expectedOwners = @("konrad-jamrozik", "weshaggard", "benbp")
+      },
+      @{
+        # The $PSScriptRoot is assumed to be azure-sdk-tools/eng/common-tests/get-codeowners/get-codeowners.tests.ps1
+        CodeownersPath = "$PSScriptRoot/../../../tools/code-owners-parser/Azure.Sdk.Tools.RetrieveCodeOwners.Tests/TestData/test_CODEOWNERS"; 
+        targetPath = "tools/code-owners-parser/Azure.Sdk.Tools.RetrieveCodeOwners.Tests/TestData/InputDir/a.txt"; 
+        expectedOwners = @("2star")
+      }      
+    ) {
+      $resolvedCodeownersPath = (Resolve-Path $codeownersPath)
+      TestGetCodeowners `
+        -TargetPath $targetPath `
+        -CodeownersFileLocation $resolvedCodeownersPath `
+        -ExpectedOwners $expectedOwners
+    }
+}
\ No newline at end of file
diff --git a/eng/common/pipelines/templates/stages/archetype-sdk-tool-pwsh.yml b/eng/common/pipelines/templates/stages/archetype-sdk-tool-pwsh.yml
index e01694adf03..5d78b132e26 100644
--- a/eng/common/pipelines/templates/stages/archetype-sdk-tool-pwsh.yml
+++ b/eng/common/pipelines/templates/stages/archetype-sdk-tool-pwsh.yml
@@ -15,20 +15,21 @@ variables:
   - template: /eng/pipelines/templates/variables/globals.yml
 
 stages:
-  - stage: 'eng_script_tests'
+  - stage:
+    displayName: Run PowerShell Tests
     jobs:
-      - job: 'Test'
+      - job: Test
         strategy:
           matrix:
             Windows:
-              Pool: 'azsdk-pool-mms-win-2022-general'
-              Image: 'windows-2022'
+              Pool: azsdk-pool-mms-win-2022-general
+              Image: windows-2022
             Linux:
               Pool: azsdk-pool-mms-ubuntu-2204-general
               Image: MMSUbuntu22.04
             Mac:
-              Pool: 'Azure Pipelines'
-              Image: 'macos-11'
+              Pool: Azure Pipelines
+              Image: macos-11
 
         pool:
           name: $(Pool)
diff --git a/eng/common/pipelines/templates/steps/run-pester-tests.yml b/eng/common/pipelines/templates/steps/run-pester-tests.yml
index 02082a6470b..ce42f65b646 100644
--- a/eng/common/pipelines/templates/steps/run-pester-tests.yml
+++ b/eng/common/pipelines/templates/steps/run-pester-tests.yml
@@ -13,7 +13,7 @@ parameters:
 
 steps:
   - pwsh: |
-     Install-Module -Name Pester -Force
+       Install-Module -Name Pester -Force
     displayName: Install Pester
 
    # default test steps
@@ -30,8 +30,10 @@ steps:
           $config.Filter.Tag = $tags
         }
 
+        Write-Host "Calling 'Invoke-Pester' in workingDirectory '$(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}'. Pester tags filter: '$tags'"
+        # https://pester.dev/docs/commands/Invoke-Pester
         Invoke-Pester -Configuration $config
-      displayName: Run Tests
+      displayName: Run Pester Tests
       env: ${{ parameters.EnvVars }}
       workingDirectory: $(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}
 
@@ -39,17 +41,17 @@ steps:
     - ${{ parameters.CustomTestSteps }}
 
   - task: PublishTestResults@2
-    displayName: 'Publish Test Results'
+    displayName: Publish Test Results
     condition: succeededOrFailed()
     inputs:
-      testResultsFormat: 'NUnit'
+      testResultsFormat: NUnit
       testResultsFiles: $(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}/testResults.xml
-      testRunTitle: '$(System.StageName)_$(Agent.JobName)_Tests'
+      testRunTitle: $(System.StageName)_$(Agent.JobName)_Tests
 
   - task: PublishCodeCoverageResults@1
-    displayName: 'Publish Code Coverage to Azure DevOps'
+    displayName: Publish Code Coverage to Azure DevOps
     condition: succeededOrFailed()
     inputs:
-      codeCoverageTool: 'JaCoCo'
-      summaryFileLocation: '$(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}/coverage.xml'
-      pathToSources: '$(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}'
\ No newline at end of file
+      codeCoverageTool: JaCoCo
+      summaryFileLocation: $(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}/coverage.xml
+      pathToSources: $(Build.SourcesDirectory)/${{ parameters.TargetDirectory }}
\ No newline at end of file
diff --git a/eng/common/scripts/get-codeowners.lib.ps1 b/eng/common/scripts/get-codeowners.lib.ps1
new file mode 100644
index 00000000000..c34f28bb225
--- /dev/null
+++ b/eng/common/scripts/get-codeowners.lib.ps1
@@ -0,0 +1,133 @@
+function Get-CodeownersTool([string] $ToolPath, [string] $DevOpsFeed, [string] $ToolVersion)
+{
+  $codeownersToolCommand = Join-Path $ToolPath "retrieve-codeowners"
+  # Check if the retrieve-codeowners tool exists or not.
+  if (Get-Command $codeownersToolCommand -errorAction SilentlyContinue) {
+    return $codeownersToolCommand
+  }
+  if (!(Test-Path $ToolPath)) {
+    New-Item -ItemType Directory -Path $ToolPath | Out-Null
+  }
+  Write-Host "Installing the retrieve-codeowners tool under tool path: $ToolPath ..."
+
+  # Run command under tool path to avoid dotnet tool install command checking .csproj files. 
+  # This is a bug for dotnet tool command. Issue: https://github.com/dotnet/sdk/issues/9623
+  Push-Location $ToolPath
+  dotnet tool install --tool-path $ToolPath --add-source $DevOpsFeed --version $ToolVersion "Azure.Sdk.Tools.RetrieveCodeOwners" | Out-Null
+  Pop-Location
+  # Test to see if the tool properly installed.
+  if (!(Get-Command $codeownersToolCommand -errorAction SilentlyContinue)) {
+    Write-Error "The retrieve-codeowners tool is not properly installed. Please check your tool path: $ToolPath"
+    return 
+  }
+  return $codeownersToolCommand
+}
+
+<#
+.SYNOPSIS
+A function that given as input $TargetPath param, returns the owners
+of that path, as determined by CODEOWNERS file passed in $CodeownersFileLocation
+param.
+
+.PARAMETER TargetPath
+Required*. Path to file or directory whose owners are to be determined from a 
+CODEOWNERS file. e.g. sdk/core/azure-amqp/ or sdk/core/foo.txt.
+
+*for backward compatibility, you might provide $TargetDirectory instead.
+
+.PARAMETER TargetDirectory
+Obsolete. Replaced by $TargetPath. Kept for backward-compatibility.
+If both $TargetPath and $TargetDirectory are provided, $TargetDirectory is
+ignored.
+
+.PARAMETER CodeownersFileLocation
+Optional. An absolute path to the CODEOWNERS file against which the $TargetPath param
+will be checked to determine its owners.
+
+.PARAMETER ToolVersion
+Optional. The NuGet package version of the package containing the "retrieve-codeowners" 
+tool, around which this script is a wrapper.
+
+.PARAMETER ToolPath
+Optional. The place to check the "retrieve-codeowners" tool existence.
+
+.PARAMETER DevOpsFeed
+Optional. The NuGet package feed from which the "retrieve-codeowners" tool is to be installed.
+
+NuGet feed:
+https://dev.azure.com/azure-sdk/public/_artifacts/feed/azure-sdk-for-net/NuGet/Azure.Sdk.Tools.RetrieveCodeOwners
+
+Pipeline publishing the NuGet package to the feed, "tools - code-owners-parser":
+https://dev.azure.com/azure-sdk/internal/_build?definitionId=3188
+
+.PARAMETER VsoVariable 
+Optional. If provided, the determined owners, based on $TargetPath matched against CODEOWNERS file at $CodeownersFileLocation, 
+will be output to Azure DevOps pipeline log as variable named $VsoVariable.
+
+Reference:
+https://learn.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch
+https://learn.microsoft.com/en-us/azure/devops/pipelines/scripts/logging-commands?view=azure-devops&tabs=bash#logging-command-format
+
+.PARAMETER IncludeNonUserAliases
+Optional. Whether to include in the returned owners list aliases that are team aliases, e.g. Azure/azure-sdk-team
+
+.PARAMETER Test
+Optional. Whether to run the script against hard-coded tests.
+
+#>
+function Get-Codeowners(
+  [string] $TargetPath,
+  [string] $TargetDirectory,
+  [string] $ToolPath = (Join-Path ([System.IO.Path]::GetTempPath()) "codeowners-tool"),
+  [string] $DevOpsFeed = "https://pkgs.dev.azure.com/azure-sdk/public/_packaging/azure-sdk-for-net/nuget/v3/index.json",
+  [string] $ToolVersion = "1.0.0-dev.20230306.3",
+  [string] $VsoVariable = "",
+  [string] $CodeownersFileLocation = "",
+  [switch] $IncludeNonUserAliases
+  )
+{
+  if ([string]::IsNullOrWhiteSpace($CodeownersFileLocation)) {
+    # The $PSScriptRoot is assumed to be azure-sdk-tools/eng/common/scripts/get-codeowners.ps1
+    $CodeownersFileLocation = (Resolve-Path $PSScriptRoot/../../../.github/CODEOWNERS)
+  }
+
+  # Backward compatibility: if $TargetPath is not provided, fall-back to the legacy $TargetDirectory
+  if ([string]::IsNullOrWhiteSpace($TargetPath)) {
+    $TargetPath = $TargetDirectory
+  }
+  if ([string]::IsNullOrWhiteSpace($TargetPath)) {
+    Write-Error "TargetPath (or TargetDirectory) parameter must be neither null nor whitespace."
+    return ,@()
+  }
+
+  $codeownersToolCommand = Get-CodeownersTool -ToolPath $ToolPath -DevOpsFeed $DevOpsFeed -ToolVersion $ToolVersion
+  Write-Host "Executing: & $codeownersToolCommand --target-path $TargetPath --codeowners-file-path-or-url $CodeownersFileLocation --exclude-non-user-aliases:$(!$IncludeNonUserAliases)"
+  $commandOutput = & $codeownersToolCommand `
+      --target-path $TargetPath `
+      --codeowners-file-path-or-url $CodeownersFileLocation `
+      --exclude-non-user-aliases:$(!$IncludeNonUserAliases) `
+      2>&1
+
+  if ($LASTEXITCODE -ne 0) {
+    Write-Host "Command $codeownersToolCommand execution failed (exit code = $LASTEXITCODE). Output string: $commandOutput"
+    return ,@()
+  } else
+  {
+    Write-Host "Command $codeownersToolCommand executed successfully (exit code = 0). Command output string length: $($commandOutput.length)"
+  }
+
+# Assert: $commandOutput is a valid JSON representing:
+# - a single CodeownersEntry, if the $TargetPath was a single path
+# - or a dictionary of CodeownerEntries, keyes by each path resolved from a $TargetPath glob path.
+#
+# For implementation details, see Azure.Sdk.Tools.RetrieveCodeOwners.Program.Main
+
+$codeownersJson = $commandOutput | ConvertFrom-Json
+  
+  if ($VsoVariable) {
+    $codeowners = $codeownersJson.Owners -join ","
+    Write-Host "##vso[task.setvariable variable=$VsoVariable;]$codeowners"
+  }
+
+  return ,@($codeownersJson.Owners)
+}
\ No newline at end of file
diff --git a/eng/common/scripts/get-codeowners.ps1 b/eng/common/scripts/get-codeowners.ps1
index a4a18ecea42..b40f9b4fa29 100644
--- a/eng/common/scripts/get-codeowners.ps1
+++ b/eng/common/scripts/get-codeowners.ps1
@@ -1,177 +1,18 @@
 <#
 .SYNOPSIS
-A script that given as input $TargetPath param, returns the owners
-of that path, as determined by CODEOWNERS file passed in $CodeOwnersFileLocation
-param.
-
-.PARAMETER TargetPath
-Required*. Path to file or directory whose owners are to be determined from a 
-CODEOWNERS file. e.g. sdk/core/azure-amqp/ or sdk/core/foo.txt.
-
-*for backward compatibility, you might provide $TargetDirectory instead.
-
-.PARAMETER TargetDirectory
-Obsolete. Replaced by $TargetPath. Kept for backward-compatibility.
-If both $TargetPath and $TargetDirectory are provided, $TargetDirectory is
-ignored.
-
-.PARAMETER CodeOwnerFileLocation
-Optional. An absolute path to the CODEOWNERS file against which the $TargetPath param
-will be checked to determine its owners.
-
-.PARAMETER ToolVersion
-Optional. The NuGet package version of the package containing the "retrieve-codeowners" 
-tool, around which this script is a wrapper.
-
-.PARAMETER ToolPath
-Optional. The place to check the "retrieve-codeowners" tool existence.
-
-.PARAMETER DevOpsFeed
-Optional. The NuGet package feed from which the "retrieve-codeowners" tool is to be installed.
-
-NuGet feed:
-https://dev.azure.com/azure-sdk/public/_artifacts/feed/azure-sdk-for-net/NuGet/Azure.Sdk.Tools.RetrieveCodeOwners
-
-Pipeline publishing the NuGet package to the feed, "tools - code-owners-parser":
-https://dev.azure.com/azure-sdk/internal/_build?definitionId=3188
-
-.PARAMETER VsoVariable 
-Optional. If provided, the determined owners, based on $TargetPath matched against CODEOWNERS file at $CodeOwnerFileLocation, 
-will be output to Azure DevOps pipeline log as variable named $VsoVariable.
-
-Reference:
-https://learn.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch
-https://learn.microsoft.com/en-us/azure/devops/pipelines/scripts/logging-commands?view=azure-devops&tabs=bash#logging-command-format
-
-.PARAMETER IncludeNonUserAliases
-Optional. Whether to include in the returned owners list aliases that are team aliases, e.g. Azure/azure-sdk-team
-
-.PARAMETER Test
-Optional. Whether to run the script against hard-coded tests.
-
+Please see the comment on Get-Codeowners defined in ./get-codeowners.lib.ps1 
 #>
 param (
-  [string]$TargetPath = "",
-  [string]$TargetDirectory = "",
-  # The path used assumes the script is located in azure-sdk-tools/eng/common/scripts/get-codeowners.ps1
-  [string]$CodeOwnerFileLocation = (Resolve-Path $PSScriptRoot/../../../.github/CODEOWNERS),
-  # The $ToolVersion 1.0.0-dev.20230214.3 includes following PR:
-  #    Use CodeownersFile.UseRegexMatcherDefault everywhere where applicable + remove obsolete tests
-  #    https://github.com/Azure/azure-sdk-tools/pull/5437
-  # 
-  # but not this one:
-  #    Remove the obsolete, prefix-based CODEOWNERS matcher & related tests
-  #    https://github.com/Azure/azure-sdk-tools/pull/5431
-  [string]$ToolVersion = "1.0.0-dev.20230223.4",
-  [string]$ToolPath = (Join-Path ([System.IO.Path]::GetTempPath()) "codeowners-tool-path"),
-  [string]$DevOpsFeed = "https://pkgs.dev.azure.com/azure-sdk/public/_packaging/azure-sdk-for-net/nuget/v3/index.json",
-  [string]$VsoVariable = "",
-  [switch]$IncludeNonUserAliases,
-  [switch]$Test
+  [string] $TargetPath = "",
+  [string] $TargetDirectory = "",
+  [string] $CodeownersFileLocation = "",
+  [switch] $IncludeNonUserAliases
 )
 
-function Get-CodeownersTool()
-{
-  $codeownersToolCommand = Join-Path $ToolPath "retrieve-codeowners"
-  # Check if the retrieve-codeowners tool exists or not.
-  if (Get-Command $codeownersToolCommand -errorAction SilentlyContinue) {
-    return $codeownersToolCommand
-  }
-  if (!(Test-Path $ToolPath)) {
-    New-Item -ItemType Directory -Path $ToolPath | Out-Null
-  }
-  Write-Host "Installing the retrieve-codeowners tool under tool path: $ToolPath ..."
-
-  # Run command under tool path to avoid dotnet tool install command checking .csproj files. 
-  # This is a bug for dotnet tool command. Issue: https://github.com/dotnet/sdk/issues/9623
-  Push-Location $ToolPath
-  dotnet tool install --tool-path $ToolPath --add-source $DevOpsFeed --version $ToolVersion "Azure.Sdk.Tools.RetrieveCodeOwners" | Out-Null
-  Pop-Location
-  # Test to see if the tool properly installed.
-  if (!(Get-Command $codeownersToolCommand -errorAction SilentlyContinue)) {
-    Write-Error "The retrieve-codeowners tool is not properly installed. Please check your tool path: $ToolPath"
-    return 
-  }
-  return $codeownersToolCommand
-}
-
-function Get-Codeowners(
-  [string]$targetPath,
-  [string]$targetDirectory,
-  [string]$codeownersFileLocation,
-  [bool]$includeNonUserAliases = $false)
-{
-  # Backward compaitiblity: if $targetPath is not provided, fall-back to the legacy $targetDirectory
-  if ([string]::IsNullOrWhiteSpace($targetPath)) {
-    $targetPath = $targetDirectory
-  }
-  if ([string]::IsNullOrWhiteSpace($targetPath)) {
-    Write-Error "TargetPath (or TargetDirectory) parameter must be neither null nor whitespace."
-    return ,@()
-  }
-
-  $codeownersToolCommand = Get-CodeownersTool
-  Write-Host "Executing: & $codeownersToolCommand --target-path $targetPath --codeowners-file-path-or-url $codeownersFileLocation --exclude-non-user-aliases:$(!$includeNonUserAliases)"
-  $commandOutput = & $codeownersToolCommand `
-      --target-path $targetPath `
-      --codeowners-file-path-or-url $codeownersFileLocation `
-      --exclude-non-user-aliases:$(!$includeNonUserAliases) `
-      2>&1
-
-  if ($LASTEXITCODE -ne 0) {
-    Write-Host "Command $codeownersToolCommand execution failed (exit code = $LASTEXITCODE). Output string: $commandOutput"
-    return ,@()
-  } else
-  {
-    Write-Host "Command $codeownersToolCommand executed successfully (exit code = 0). Output string length: $($commandOutput.length)"
-  }
-
-# Assert: $commandOutput is a valid JSON representing:
-# - a single CodeownersEntry, if the $targetPath was a single path
-# - or a dictionary of CodeownerEntries, keyes by each path resolved from a $targetPath glob path.
-#
-# For implementation details, see Azure.Sdk.Tools.RetrieveCodeOwners.Program.Main
-
-$codeownersJson = $commandOutput | ConvertFrom-Json
-  
-  if ($VsoVariable) {
-    $codeowners = $codeownersJson.Owners -join ","
-    Write-Host "##vso[task.setvariable variable=$VsoVariable;]$codeowners"
-  }
-
-  return ,@($codeownersJson.Owners)
-}
-
-function TestGetCodeowners([string]$targetPath, [string]$codeownersFileLocation, [bool]$includeNonUserAliases = $false, [string[]]$expectReturn) {
-  Write-Host "Test: find owners matching '$targetPath' ..."
-  
-  $actualReturn = Get-Codeowners -targetPath $targetPath -codeownersFileLocation $codeownersFileLocation -includeNonUserAliases $IncludeNonUserAliases
-
-  if ($actualReturn.Count -ne $expectReturn.Count) {
-    Write-Error "The length of actual result is not as expected. Expected length: $($expectReturn.Count), Actual length: $($actualReturn.Count)."
-    exit 1
-  }
-  for ($i = 0; $i -lt $expectReturn.Count; $i++) {
-    if ($expectReturn[$i] -ne $actualReturn[$i]) {
-      Write-Error "Expect result $expectReturn[$i] is different than actual result $actualReturn[$i]."
-      exit 1
-    }
-  }
-}
-
-if ($Test) {
-  # Most of tests here have been removed; now instead we should run tests from RetrieveCodeOwnersProgramTests, and in a way as explained in:
-  # https://github.com/Azure/azure-sdk-tools/issues/5434
-  # https://github.com/Azure/azure-sdk-tools/pull/5103#discussion_r1068680818
-  Write-Host "Running reduced test suite at `$PSScriptRoot of $PSSCriptRoot. Please see https://github.com/Azure/azure-sdk-tools/issues/5434 for more."
+. $PSScriptRoot/get-codeowners.lib.ps1
 
-  $azSdkToolsCodeowners = (Resolve-Path "$PSScriptRoot/../../../.github/CODEOWNERS")
-  TestGetCodeowners -targetPath "eng/common/scripts/get-codeowners.ps1" -codeownersFileLocation $azSdkToolsCodeowners -includeNonUserAliases $true -expectReturn @("konrad-jamrozik", "weshaggard", "benbp")
-  
-  $testCodeowners = (Resolve-Path "$PSScriptRoot/../../../tools/code-owners-parser/Azure.Sdk.Tools.RetrieveCodeOwners.Tests/TestData/test_CODEOWNERS")
-  TestGetCodeowners -targetPath "tools/code-owners-parser/Azure.Sdk.Tools.RetrieveCodeOwners.Tests/TestData/InputDir/a.txt" -codeownersFileLocation $testCodeowners -includeNonUserAliases $true -expectReturn @("2star")
-  exit 0
-}
-else {
-  return Get-Codeowners -targetPath $TargetPath -targetDirectory $TargetDirectory -codeownersFileLocation $CodeOwnerFileLocation -includeNonUserAliases $IncludeNonUserAliases
-}
+return Get-Codeowners `
+  -TargetPath $TargetPath `
+  -TargetDirectory $TargetDirectory `
+  -CodeownersFileLocation $CodeownersFileLocation `
+  -IncludeNonUserAliases:$IncludeNonUserAliases
\ No newline at end of file
diff --git a/tools/code-owners-parser/CodeOwnersParser.sln b/tools/code-owners-parser/CodeOwnersParser.sln
index fc4b2530a2f..8fa63a1ca1c 100644
--- a/tools/code-owners-parser/CodeOwnersParser.sln
+++ b/tools/code-owners-parser/CodeOwnersParser.sln
@@ -12,10 +12,12 @@ EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{EF585CCA-55F8-44EB-921A-30996CBAFC49}"
 	ProjectSection(SolutionItems) = preProject
 		ci.yml = ci.yml
+		..\..\eng\common\scripts\get-codeowners.lib.ps1 = ..\..\eng\common\scripts\get-codeowners.lib.ps1
 		..\..\eng\common\scripts\get-codeowners.ps1 = ..\..\eng\common\scripts\get-codeowners.ps1
+		..\..\eng\common-tests\get-codeowners\get-codeowners.tests.ps1 = ..\..\eng\common-tests\get-codeowners\get-codeowners.tests.ps1
 	EndProjectSection
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Azure.Sdk.Tools.CodeOwnersParser.Tests", "Azure.Sdk.Tools.CodeOwnersParser.Tests\Azure.Sdk.Tools.CodeOwnersParser.Tests.csproj", "{66C9FF6A-32DD-4C3C-ABE1-F1F58C1C8129}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Azure.Sdk.Tools.CodeOwnersParser.Tests", "Azure.Sdk.Tools.CodeOwnersParser.Tests\Azure.Sdk.Tools.CodeOwnersParser.Tests.csproj", "{66C9FF6A-32DD-4C3C-ABE1-F1F58C1C8129}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
diff --git a/tools/code-owners-parser/ci.yml b/tools/code-owners-parser/ci.yml
index c881b799702..d28af6b9058 100644
--- a/tools/code-owners-parser/ci.yml
+++ b/tools/code-owners-parser/ci.yml
@@ -20,17 +20,14 @@ pr:
   paths:
     include:
       - tools/code-owners-parser
-      - eng/common/scripts/get-codeowners.ps1
+      - eng/common/scripts/get-codeowners
 
 extends:
   template: /eng/pipelines/templates/stages/archetype-sdk-tool-dotnet.yml
   parameters:
     ToolDirectory: tools/code-owners-parser
     TestPostSteps:
-      - task: PowerShell@2
-        displayName: Test on code owner script
-        inputs:
-          pwsh: true
-          filePath: eng/common/scripts/get-codeowners.ps1
-          arguments: >
-            -Test
\ No newline at end of file
+      - template: /eng/common/pipelines/templates/steps/run-pester-tests.yml
+        parameters:
+          TargetDirectory: eng/common-tests/get-codeowners
+          TargetTags: UnitTest
\ No newline at end of file