(chocolatey#3381) Add Pester tests for rule command

The next release includes a new choco rule command, that allows
displaying information about the validation rules that are currently in
use by Chocolatey CLI.

This commit adds basic Pester tests for exercising this command, along
with its subcommands.

tests/pester-tests/commands/choco-rule.Tests.ps1

@@ -0,0 +1,92 @@
+Import-Module helpers/common-helpers
+
+Describe "choco rule" -Tag Chocolatey, RuleCommand {
+    BeforeDiscovery {
+    }
+
+    BeforeAll {
+        Remove-NuGetPaths
+        Initialize-ChocolateyTestInstall
+
+        New-ChocolateyInstallSnapshot
+    }
+
+    AfterAll {
+        Remove-ChocolateyTestInstall
+    }
+
+    Context "Running without subcommand specified" {
+        BeforeAll {
+            Restore-ChocolateyInstallSnapshot
+
+            $Output = Invoke-Choco rule
+        }
+
+        It "Exits with Success (0)" {
+            $Output.ExitCode | Should -Be 0 -Because $Output.String
+        }
+
+        It "Displays the rules expected" {
+            $Output.Lines | Should -Contain 'CHCR0001: A required element is missing or has no content in the package nuspec file.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCR0002: Enabling license acceptance requires a license url.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCU0001: The specified content of the element is not of the expected type and can not be accepted.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCU0002: Unsupported element is used.' -Because $Output.String
+        }
+    }
+
+    Context "Running with list subcommand" {
+        BeforeAll {
+            Restore-ChocolateyInstallSnapshot
+
+            $Output = Invoke-Choco rule list
+        }
+
+        It "Exits with Success (0)" {
+            $Output.ExitCode | Should -Be 0 -Because $Output.String
+        }
+
+        It "Displays the rules expected" {
+            $Output.Lines | Should -Contain 'CHCR0001: A required element is missing or has no content in the package nuspec file.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCR0002: Enabling license acceptance requires a license url.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCU0001: The specified content of the element is not of the expected type and can not be accepted.' -Because $Output.String
+            $Output.Lines | Should -Contain 'CHCU0002: Unsupported element is used.' -Because $Output.String
+        }
+    }
+
+    Context "Running with get subcommand specified with no additional parameters" {
+        BeforeAll {
+            Restore-ChocolateyInstallSnapshot
+
+            $Output = Invoke-Choco rule get
+        }
+
+        It "Exits with Failure (1)" {
+            $Output.ExitCode | Should -Be 1 -Because $Output.String
+        }
+
+        It "Displays error with correct format" {
+            $Output.Lines | Should -Contain "A Rule Name (-n|--name) is required when getting information for a specific rule." -Because $Output.String
+        }
+    }
+
+    Context "Running with get subcommand specified with --name parameter" {
+        BeforeAll {
+            Restore-ChocolateyInstallSnapshot
+
+            $Output = Invoke-Choco rule get --name CHCU0001
+        }
+
+        It "Exits with Success (0)" {
+            $Output.ExitCode | Should -Be 0 -Because $Output.String
+        }
+
+        It "Displays rule information" {
+            $Output.Lines | Should -Contain "Name: CHCU0001 | Severity: Error" -Because $Output.String
+            $Output.Lines | Should -Contain "Summary: The specified content of the element is not of the expected type and can not be accepted." -Because $Output.String
+            $Output.Lines | Should -Contain "Help URL:" -Because $Output.String
+        }
+    }
+
+    # This needs to be the last test in this block, to ensure NuGet configurations aren't being created.
+    Test-NuGetPaths
+}