Stravaig Logging Diagnostics

Diagnostics for examining logs in automated tests.

Injecting a logger to the class under test

If you just need to inject a logger into the class you are testing then you can simply create an instance of a TestCaptureLogger and inject it in.

For example, say you need to test a service class that takes a logger. The class might look something like this:

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public class MyService
{
  private readonly ILogger<MyService> _logger;

  public MyService(ILogger<MyService> logger)
  {
    _logger = logger;
  }

  public void DoStuff()
  {
    // Do whatever the service needs to do.
    _logger.LogInformation("The work is done.");
  }
}

To test that the logger was called with the relevant message you can create a test like this:

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[Test]
public void TestServiceLoggerCalled()
{
  // Arrange
  var logger = new TestCaptureLogger<MyService>();
  var service = new MyService(logger);

  // Act
  service.DoStuff();

  // Assert
  var logs = logger.GetLogs();
  logs.Count.ShouldBe(1);
  logs[0].FormattedMessage.ShouldContain("The work is done.");
}

Note: The above example uses NUnit as the test framework, and Shouldly as the assertion framework.