MELT 0.2.0

Testing Library for Microsoft Extensions Logging.

About MELT

MELT is a free, open source, testing library for the .NET Standard Microsoft Extensions Logging library. It is a solution to easily test logs.

It is a repackaging with a sweetened API and some omissions of Microsoft.Extensions.Logging.Testing, a library used internally in ASP.NET Core for testing the logging, given that there is currently no plan to offer an official package for it.

It is licensed under Apache License 2.0. Most of the code is copyrighted by the .NET Foundation as mentioned in the files headers.

If you like this project please don't forget to star it on GitHub or let me know with a tweet.

Quick start

• Install the NuGet package MELT

  <PackageReference Include="MELT" Version="0.1.0" />
  

• Get a test logger factory

  var loggerFactory = MELTBuilder.CreateLoggerFactory();
  

• Get a logger from the factory as usual, to pass ro your fixture.

  var logger = loggerFactory.CreateLogger<Sample>();
  

Assert log entries

The logger factory expose a property LogEntries that enumerates all the logs captured. Each entry expose all the relevant property for a log.

For example, to test with xUnit that a single log has been emitted and it had a specific message:

var log = Assert.Single(loggerFactory.LogEntries);
Assert.Equal("The answer is 42", log.Message);

Assert scopes

The logger factory expose a property Scopes that enumerates all the scopes captured.

For example, to test with xUnit that a single scope has been emitted and it had a specific message:

var scope = Assert.Single(loggerFactory.Scopes);
Assert.Equal("I'm in the GET scope", scope.Message);

There is also a property Scope in each log entry to have the scope captured with that entry.

Easily test log or scope properties with xUnit

• Install the NuGet package MELT.Xunit

  <PackageReference Include="MELT.Xunit" Version="0.1.0" />
  

• Use the LogValuesAssert.Contains(...) helpers. For example, to test that a single log has been emitted and it had a property number with value 42:

  var log = Assert.Single(loggerFactory.LogEntries);
  LogValuesAssert.Contains("number", 42, log.Properties);
  

Full example

See SampleTest.

Quick start for ASP.NET Core integration tests

• Install the NuGet package MELT

  <PackageReference Include="MELT" Version="0.1.0" />
  

• Create a test sink using MELTBuilder.CreateTestSink(...), where you can also customize the bahaviour.

  For example to filter all log entries and scopes not generated by loggers consumed in the SampleWebApplication.* namespace (this filters the logger name so it assumes you are using ILogger<T> or following the default naming convention for your loggers.)

  ITestSink _sink = MELTBuilder.CreateTestSink(options => options.FilterByNamespace(nameof(SampleWebApplication)));
  

  You can also filter by logger name using FilterByTypeName<T>() or FilterByLoggerName(string name).

• Use the AddTestLogger(...) extension method to add the test logger provider to the logging builder. This can be done where you are already configuring the web host builder.

  Configure the logger using WithWebHostBuilder on the factory.

  using using Microsoft.Extensions.Logging;
  // ...
  factory = factory.WithWebHostBuilder(builder => builder.ConfigureLogging(logging => logging.AddTestLogger(_sink)));
  

  Alternatively, you can configure the logger builder in the ConfigureWebHost implementation of your custom WebApplicationFactory<T>. If you chose so, the same sink will be used by all tests using the same factory. You can clear the sink in the test costrctuctor with Clear() if you like to have a clean state before each test, as xUnit will not run tests consuming the same fixture in parallel.

  The logger will be automatically injected with Dependency Injection.

Assert log entries

The sink expose a property LogEntries that enumerates all the logs captured. Each entry expose all the relevant property for a log.

For example, to test with xUnit that a single log has been emitted and it had a specific message:

var log = Assert.Single(sink.LogEntries);
Assert.Equal("The answer is 42", log.Message);

Assert scopes

The sink expose a property Scopes that enumerates all the scopes captured.

For example, to test with xUnit that a single scope has been emitted and it had a specific message:

var scope = Assert.Single(sink.Scopes);
Assert.Equal("I'm in the GET scope", scope.Message);

There is also a property Scope in each log entry to have the scope captured with that entry.

Easily test log or scope properties with xUnit

• Install the NuGet package MELT.Xunit

  <PackageReference Include="MELT.Xunit" Version="0.1.0" />
  

• Use the LogValuesAssert.Contains(...) helpers. For example, to test that a single log has been emitted and it had a property number with value 42:

  var log = Assert.Single(sink.LogEntries);
  LogValuesAssert.Contains("number", 42, log.Properties);
  

Full example

See LoggingTest.