Add unit tests for TestFrameworkProvider

Src/FluentAssertions/Common/Configuration.cs

@@ -5,6 +5,11 @@ namespace FluentAssertions.Common;
 
 public class Configuration
 {
+    /// <summary>
+    /// Defines the key for the configuration of the test framework to be assumed in FluentAssertions.
+    /// </summary>
+    private const string TestFrameworkConfigurationKey = "FluentAssertions.TestFramework";
+
     #region Private Definitions
 
     private readonly object propertiesAccessLock = new();
@@ -118,7 +123,7 @@ public string TestFrameworkName
         {
             if (string.IsNullOrEmpty(testFrameworkName))
             {
-                testFrameworkName = store.GetSetting("FluentAssertions.TestFramework");
+                testFrameworkName = store.GetSetting(TestFrameworkConfigurationKey);
             }
 
             return testFrameworkName;

Src/FluentAssertions/Execution/TestFrameworkProvider.cs

@@ -6,6 +6,9 @@
 
 namespace FluentAssertions.Execution;
 
+/// <summary>
+/// Implements a wrapper around all supported test frameworks to throw the correct assertion exception.
+/// </summary>
 internal static class TestFrameworkProvider
 {
     #region Private Definitions
@@ -28,24 +31,24 @@ public static void Throw(string message)
     {
         if (testFramework is null)
         {
-            testFramework = DetectFramework();
+            testFramework = DetectFramework(Services.Configuration);
         }
 
         testFramework.Throw(message);
     }
 
-    private static ITestFramework DetectFramework()
+    internal static ITestFramework DetectFramework(Configuration configuration)
     {
-        ITestFramework detectedFramework = AttemptToDetectUsingAppSetting()
+        ITestFramework detectedFramework = AttemptToDetectUsingAppSetting(configuration)
             ?? AttemptToDetectUsingDynamicScanning()
             ?? new FallbackTestFramework();
 
         return detectedFramework;
     }
 
-    private static ITestFramework AttemptToDetectUsingAppSetting()
+    internal static ITestFramework AttemptToDetectUsingAppSetting(Configuration configuration)
     {
-        string frameworkName = Services.Configuration.TestFrameworkName;
+        string frameworkName = configuration.TestFrameworkName;
         if (string.IsNullOrEmpty(frameworkName))
         {
             return null;
@@ -54,22 +57,23 @@ private static ITestFramework AttemptToDetectUsingAppSetting()
         if (!Frameworks.TryGetValue(frameworkName, out ITestFramework framework))
         {
             string frameworks = string.Join(", ", Frameworks.Keys);
-            var message = $"FluentAssertions was configured to use {frameworkName} but the requested test framework is not supported. " +
-                $"Please use one of the supported frameworks: {frameworks}";
+            var message = $"FluentAssertions was configured to use the test framework '{frameworkName}' but this is not supported. " +
+                $"Please use one of the supported frameworks: {frameworks}.";
 
-            throw new Exception(message);
+            throw new InvalidOperationException(message);
         }
 
         if (!framework.IsAvailable)
         {
             string frameworks = string.Join(", ", Frameworks.Keys);
-            var message = framework is LateBoundTestFramework lateBoundTestFramework
-                ? $"FluentAssertions was configured to use {frameworkName} but the required test framework assembly {lateBoundTestFramework.AssemblyName} could not be found. " +
-                    $"Please use one of the supported frameworks: {frameworks}"
-                : $"FluentAssertions was configured to use {frameworkName} but the required test framework could not be found. " +
-                    $"Please use one of the supported frameworks: {frameworks}";
-
-            throw new Exception(message);
+            var innerMessage = framework is LateBoundTestFramework lateBoundTestFramework
+                ? $"the required assembly '{lateBoundTestFramework.AssemblyName}' could not be found"
+                : "it could not be found";
+            var message =
+                $"FluentAssertions was configured to use the test framework '{frameworkName}' but {innerMessage}. " +
+                $"Please use one of the supported frameworks: {frameworks}.";
+
+            throw new InvalidOperationException(message);
         }
 
         return framework;

Tests/FluentAssertions.Specs/Execution/TestFrameworkProviderTests.cs

@@ -0,0 +1,81 @@
+using System;
+using FluentAssertions.Common;
+using FluentAssertions.Execution;
+using Xunit;
+
+using static FluentAssertions.FluentActions;
+
+namespace FluentAssertions.Specs.Execution;
+
+public class TestFrameworkProviderTests
+{
+    [Fact]
+    public void When_running_xunit_test_implicitly_it_should_be_detected()
+    {
+        var configuration = new Configuration(new TestConfigurationStore());
+        var result = TestFrameworkProvider.DetectFramework(configuration);
+
+        result.IsAvailable.Should().BeTrue();
+        result.Should().BeOfType<XUnit2TestFramework>();
+    }
+
+    [Fact]
+    public void When_running_xunit_test_explicitly_it_should_be_detected()
+    {
+        var configuration = new Configuration(new TestConfigurationStore())
+        {
+            TestFrameworkName = "xunit2"
+        };
+        var result = TestFrameworkProvider.DetectFramework(configuration);
+
+        result.IsAvailable.Should().BeTrue();
+        result.Should().BeOfType<XUnit2TestFramework>();
+    }
+
+    [Fact]
+    public void When_running_test_with_unknown_test_framework_it_should_throw()
+    {
+        var configuration = new Configuration(new TestConfigurationStore())
+        {
+            TestFrameworkName = "foo"
+        };
+
+        Invoking(() => TestFrameworkProvider.AttemptToDetectUsingAppSetting(configuration))
+            .Should().Throw<InvalidOperationException>()
+            .WithMessage("FluentAssertions was configured to use the test framework 'foo' but this is not supported."
+                         + " Please use one of the supported frameworks: mspec, nspec3, nunit, mstestv2, xunit2.");
+    }
+
+    [Fact]
+    public void When_running_test_with_direct_bound_but_unavailable_test_framework_it_should_throw()
+    {
+        var configuration = new Configuration(new TestConfigurationStore())
+        {
+            TestFrameworkName = "nspec3"
+        };
+
+        Invoking(() => TestFrameworkProvider.AttemptToDetectUsingAppSetting(configuration))
+            .Should().Throw<InvalidOperationException>()
+            .WithMessage("FluentAssertions was configured to use the test framework 'nspec3' but it could not be found."
+                         + " Please use one of the supported frameworks: mspec, nspec3, nunit, mstestv2, xunit2.");
+    }
+
+    [Fact]
+    public void When_running_test_with_late_bound_but_unavailable_test_framework_it_should_throw()
+    {
+        var configuration = new Configuration(new TestConfigurationStore())
+        {
+            TestFrameworkName = "nunit"
+        };
+
+        Invoking(() => TestFrameworkProvider.AttemptToDetectUsingAppSetting(configuration))
+            .Should().Throw<InvalidOperationException>()
+            .WithMessage("FluentAssertions was configured to use the test framework 'nunit' but the required assembly 'nunit.framework' could not be found."
+                         + " Please use one of the supported frameworks: mspec, nspec3, nunit, mstestv2, xunit2.");
+    }
+
+    private sealed class TestConfigurationStore : IConfigurationStore
+    {
+        string IConfigurationStore.GetSetting(string name) => string.Empty;
+    }
+}