Add tests for cmdlet example

docs/cmdlet-example/SendGreeting.Tests.ps1

@@ -0,0 +1,13 @@
+Describe "Send-Greeting cmdlet" {
+    It "Should be able build the cmdlet" {
+        Remove-Item -Recurse -Force bin -ErrorAction SilentlyContinue
+        dotnet restore --verbosity Error | Should BeNullOrEmpty
+        dotnet build | ?{ $_ -match "Compiling SendGreeting for .NETStandard,Version=v1.5" } | Should Not BeNullOrEmpty
+    }
+
+    It "Should be able to use the module" {
+        Import-Module -ErrorAction Stop ./bin/Debug/netstandard1.5/SendGreeting.dll
+        Send-Greeting -Name World | Should Be "Hello World!"
+        Remove-Module SendGreeting
+    }
+}