You will need to have created and opened an analyzer project, say CSharpAnalyzers in Visual Studio 2017. Refer to the first recipe in this chapter to create this project.

[TestMethod]
public void TestMethod1()
{
  var test = @"class Class1 { }";

  VerifyCSharpDiagnostic(test);
}

var expected = new DiagnosticResult
{
  Id = "CSharpAnalyzers",
  Message = String.Format("Type name '{0}' contains lowercase letters", "Class1"),
  Severity = DiagnosticSeverity.Warning,
  Locations = new[] {
    new DiagnosticResultLocation("Test0.cs", 11, 15)
  }
};

VerifyCSharpDiagnostic(test, expected);

new DiagnosticResultLocation("Test0.cs", 11, 7)

var test = @"class CLASS1 { }";

 var test = @"class CLASS1 { }";

 VerifyCSharpDiagnostic(test);

The analyzer unit test project allows us to write unit tests for the execution of our analyzer on different code samples. Each unit test is marked with a TestMethod attribute and defines sample test code, expected diagnostic(s) reported by the analyzer on that code (if any), and invocation of test helper method(s), here VerifyCSharpDiagnostic, to verify diagnostics.

//No diagnostics expected to show up
[TestMethod]
public void TestMethod1()
{
  var test = @"";

  VerifyCSharpDiagnostic(test);
}

Unit tests can define expected diagnostics using the DiagnosticResult type, which must specify the diagnostic Id, Message, Severity and Locations for the diagnostic:

var expected = new DiagnosticResult
{
  Id = "CSharpAnalyzers",
  Message = String.Format("Type name '{0}' contains lowercase letters", "Class1"),
  Severity = DiagnosticSeverity.Warning,
  Locations = new[] { new DiagnosticResultLocation("Test0.cs", 11, 15) }
};

VerifyCSharpDiagnostic(test, expected);

UnitTest type containing all the unit tests also overrides the following methods to return the DiagnosticAnalyzer (and optionally a CodeFixProvider) to be tested:

 protected override CodeFixProvider GetCSharpCodeFixProvider()
 {
   return new CSharpAnalyzersCodeFixProvider();
 }

protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
 {
   return new CSharpAnalyzersAnalyzer();
 }

Now, let us expand a bit more on the test framework helpers for the unit tests. The analyzer unit test project contains two primary helper abstract types to write unit tests for analyzers and code fixes:

In the default analyzer project, UnitTest type derives from CodeFixVerifier, but could also be changed to derive from DiagnosticVerifier, if you are only interested in writing analyzer unit tests. We will just focus on the DiagnosticVerifier here; CodeFixVerifier is covered later in chapter.

DiagnosticVerifier type is split into 2 source files DiagnosticVerifier.cs and DiagnosticVerifier.Helper.cs.

Live Unit testing is a new feature in Visual Studio 2017 Enterprise Edition, which automatically runs the impacted unit tests in the background as you edit code, and visualizes the results and code coverage live, in the editor, in real-time. Refer to Chapter 6, Live Unit Testing in Visual Studio Enterprise, to enable live unit testing for the project and visualize unit tests automatically executing after you edit the code in the steps in this recipe.