Add functional tests of AddSerilog() extension method.

Author: agehrke

test/Serilog.Extensions.Logging.Tests/SerilogLoggingBuilderExtensionsTests.cs

@@ -0,0 +1,56 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Serilog.Extensions.Logging.Tests.Support;
+using Xunit;
+
+namespace Serilog.Extensions.Logging.Tests;
+
+public class SerilogLoggingBuilderExtensionsTests
+{
+    [Fact]
+    public void AddSerilog_must_register_a_ILoggerProvider()
+    {
+        var services = new ServiceCollection()
+            .AddLogging(builder => { builder.AddSerilog(); })
+            .BuildServiceProvider();
+
+        var loggerProviders = services.GetServices<ILoggerProvider>();
+        Assert.Contains(loggerProviders, provider => provider is SerilogLoggerProvider);
+    }
+
+    [Fact]
+    public void AddSerilog_must_register_a_ILoggerProvider_that_forwards_logs_to_static_Serilog_Logger()
+    {
+        var sink = new SerilogSink();
+        Log.Logger = new LoggerConfiguration()
+            .WriteTo.Sink(sink)
+            .CreateLogger();
+
+        var services = new ServiceCollection()
+            .AddLogging(builder => { builder.AddSerilog(); })
+            .BuildServiceProvider();
+
+        var logger = services.GetRequiredService<ILogger<SerilogLoggingBuilderExtensionsTests>>();
+        logger.LogInformation("Hello, world!");
+
+        Assert.Single(sink.Writes);
+    }
+
+    [Fact]
+    public void AddSerilog_must_register_a_ILoggerProvider_that_forwards_logs_to_provided_logger()
+    {
+        var sink = new SerilogSink();
+        var serilogLogger = new LoggerConfiguration()
+            .WriteTo.Sink(sink)
+            .CreateLogger();
+
+        var services = new ServiceCollection()
+            .AddLogging(builder => { builder.AddSerilog(logger: serilogLogger); })
+            .BuildServiceProvider();
+
+        var logger = services.GetRequiredService<ILogger<SerilogLoggingBuilderExtensionsTests>>();
+        logger.LogInformation("Hello, world!");
+
+        Assert.Single(sink.Writes);
+    }
+}