Add tests for FallbackTestFramework and AssertionFailedException

Tests/FluentAssertions.Specs/Execution/FallbackTestFrameworkTests.cs

@@ -0,0 +1,24 @@
+using FluentAssertions.Execution;
+using Xunit;
+
+namespace FluentAssertions.Specs.Execution;
+
+public class FallbackTestFrameworkTests
+{
+    [Fact]
+    public void When_accessing_fallback_test_framework_it_is_always_available()
+    {
+        var sut = new FallbackTestFramework();
+
+        sut.IsAvailable.Should().BeTrue();
+    }
+
+    [Fact]
+    public void When_using_fallback_test_framework_the_correct_exception_is_thrown()
+    {
+        var sut = new FallbackTestFramework();
+
+        sut.Invoking(x => x.Throw("test message")).Should().ThrowExactly<AssertionFailedException>()
+            .WithMessage("test message");
+    }
+}