(chocolatey#3225) Add Pester Tests to ensure environment

Make use of the test-environment package that already exists to get the
environment variables set by Chocolatey and ensure that key variables
are set as they should be.

tests/chocolatey-tests/features/EnvironmentVariables.Tests.ps1

@@ -0,0 +1,43 @@
+Describe "Ensuring Chocolatey Environment variables are correct (<_>)" -ForEach @(
+    "config"
+    "cli"
+) -Tag EnvironmentVariables, Chocolatey {
+    BeforeDiscovery {
+        $TestedVariables = @(
+            @{ Name = 'TEMP' ; Value = "C:\Temp\$PID" }
+            @{ Name = 'TMP' ; Value = "C:\Temp\$PID" }
+            @{ Name = 'ChocolateyPackageFolder' ; Value = '{0}\lib\test-environment' }
+            @{ Name = 'ChocolateyPackageName' ; Value = 'test-environment' }
+            @{ Name = 'ChocolateyPackageTitle' ; Value = 'test-environment (Install)' }
+            @{ Name = 'ChocolateyPackageVersion' ; Value = '1.0.0' }
+        )
+    }
+
+    BeforeAll {
+        Initialize-ChocolateyTestInstall
+        New-ChocolateyInstallSnapshot
+        $cacheDir = "C:\Temp\$PID"
+        switch ($_) {
+            'config' {
+                Invoke-Choco config set --name=cachelocation --value $cacheDir
+            }
+            'cli' {
+                $cacheArg = "--cache-location='$cacheDir'"
+            }
+        }
+        $Output = Invoke-Choco install test-environment --version 1.0.0 $cacheArg
+    }
+
+    AfterAll {
+        Remove-ChocolateyTestInstall
+    }
+
+    It "Should exit with success (0)" {
+        $Output.ExitCode | Should -Be 0 -Because $Output.String
+    }
+
+    It 'Should Output the expected value for <Name> environment variable' -ForEach $TestedVariables {
+        $ExpectedLine = "$Name=$Value" -f $env:ChocolateyInstall
+        $Output.Lines | Should -Contain $ExpectedLine -Because $Output.String
+    }
+}