Add new opt-in common test for markdown link linting (#273)

- Add new opt-in common test for markdown link linting (issue #211).

Author: johlju

Meta.Tests.ps1

@@ -1037,3 +1037,77 @@ Describe 'Common Tests - Validate Markdown Files' -Tag 'Markdown' {
                 "to have this text execute.")
     }
 }
+
+Describe 'Common Tests - Validate Markdown Links' -Tag 'Markdown' {
+    $optIn = Get-PesterDescribeOptInStatus -OptIns $optIns
+
+    $dependencyModuleName = 'MarkdownLinkCheck'
+    $uninstallMarkdownLinkCheck = $false
+
+    Context 'When installing markdown link validation dependencies' {
+        It "Should not throw an error when installing and importing the module MarkdownLinkCheck" -Skip:(!$optIn) {
+            {
+                if (-not (Get-Module -Name $dependencyModuleName -ListAvailable))
+                {
+                    # Remember that we installed the module, so that it gets uninstalled.
+                    $uninstallMarkdownLinkCheck = $true
+                    Install-Module -Name $dependencyModuleName -Force -Scope 'CurrentUser' -ErrorAction Stop
+                }
+
+                Import-Module -Name $dependencyModuleName -Force
+            } | Should -Not -Throw
+        }
+    }
+
+    $markdownFileExtensions = @('.md')
+
+    $markdownFiles = Get-TextFilesList $moduleRootFilePath |
+        Where-Object -FilterScript {
+            $markdownFileExtensions -contains $_.Extension
+        }
+
+    foreach ($markdownFileToValidate in $markdownFiles)
+    {
+        $contextDescriptiveName = Join-Path -Path (Split-Path $markdownFileToValidate.Directory -Leaf) -ChildPath (Split-Path $markdownFileToValidate -Leaf)
+
+        Context -Name $contextDescriptiveName {
+            It "Should not contain any broken links" -Skip:(!$optIn) {
+                $getMarkdownLinkParameters = @{
+                    BrokenOnly = $true
+                    Path = $markdownFileToValidate.FullName
+                }
+
+                # Make sure it always returns an array even if Get-MarkdownLink returns $null.
+                $brokenLinks = @(Get-MarkdownLink @getMarkdownLinkParameters)
+
+                if ($brokenLinks.Count -gt 0)
+                {
+                    # Write out all the errors so the contributor can resolve.
+                    foreach ($brokenLink in $brokenLinks)
+                    {
+                        $message = 'Line {0}: [{1}] has broken URL "{2}"' -f $brokenLink.Line, $brokenLink.Text, $brokenLink.Url
+                        Write-Host -BackgroundColor Yellow -ForegroundColor Black -Object $message
+                    }
+                }
+
+                $brokenLinks.Count | Should -Be 0
+            }
+        }
+    }
+
+    if ($uninstallMarkdownLinkCheck)
+    {
+        Context 'When uninstalling markdown link validation dependencies' {
+            It "Should not throw an error when uninstalling the module MarkdownLinkCheck" -Skip:(!$optIn) {
+                {
+                    <#
+                        Remove the module from the current session as
+                        Uninstall-Module does not do that.
+                    #>
+                    Remove-Module -Name $dependencyModuleName -Force
+                    Uninstall-Module -Name $dependencyModuleName -Force -ErrorAction Stop
+                } | Should -Not -Throw
+            }
+        }
+    }
+}

README.md

@@ -41,6 +41,7 @@ This branch is used by DSC Resource Kit modules for running common tests.
 - [Example Usage of DSCResource.Tests in AppVeyor.yml](#example-usage-of-dscresourcetests-in-appveyoryml)
 - [AppVeyor Module](#appveyor-module)
   - [Phased Meta test Opt-In](#phased-meta-test-opt-in)
+    - [Common Tests - Validate Markdown Links](#common-tests---validate-markdown-links)
   - [Using AppVeyor.psm1 with the default shared model](#using-appveyorpsm1-with-the-default-shared-model)
   - [Using AppVeyor.psm1 with harness model](#using-appveyorpsm1-with-harness-model)
 - [Encrypt Credentials in Integration Tests](#encrypt-credentials-in-integration-tests)
@@ -293,6 +294,22 @@ The following opt-in flags are available:
   129 characters. 129 characters is the current (known) maximum for a relative
   path to be able to compile a configuration in Azure Automation using a
   DSC resource module.
+- **Common Tests - Validate Markdown Links**: fails tests if a link in
+  a markdown file is broken.
+
+#### Common Tests - Validate Markdown Links
+
+The test validates the links in markdown files. Any valid GitHub markdown link
+will pass the linter.
+
+>**NOTE!** There is currently a bug in the markdown link linter that makes it
+>unable to recognize absolute paths where the absolute link starts in a parent
+>folder.
+>For example, if a markdown file `/Examples/README.md`,
+>contains an absolute link pointing to `/Examples/Resources/SqlAG`,
+>that link will fail the test. Changing the link to a relative link from the
+>README.md file's folder, e.g `Resources/SqlAG` will pass the test.
+>See issue [vors/MarkdownLinkCheck#5](https://github.com/vors/MarkdownLinkCheck/issues/5).
 
 ### Using AppVeyor.psm1 with the default shared model
 
@@ -1000,6 +1017,8 @@ Contributors that add or change an example to be published must make sure that
 - Added a common tests to test the length of the relative file path so the paths
   are not exceeding the current path hard limit in Azure Automation
   ([issue #188](https://github.com/PowerShell/DscResource.Tests/issues/188)).
+- Add new opt-in common test for markdown link linting
+  ([issue #211](https://github.com/PowerShell/DscResource.Tests/issues/211)).
 
 ### 0.2.0.0