Defer adding user secrets and building configuration

examples/Xunit.Microsoft.DependencyInjection.ExampleTests/ConfigurationTests.cs

@@ -0,0 +1,22 @@
+namespace Xunit.Microsoft.DependencyInjection.ExampleTests;
+
+public class ConfigurationTests : TestBed<TestProjectFixture>
+{
+    private const string Key = "CONFIG_KEY";
+    private const string Value = "Value";
+
+    public ConfigurationTests(ITestOutputHelper testOutputHelper, TestProjectFixture fixture) : base(testOutputHelper, fixture)
+    {
+        Environment.SetEnvironmentVariable(Key, Value);
+    }
+
+    [Fact]
+    public void EnvironmentVariablesViaConstructorAreAvailable()
+    {
+        _fixture.GetServiceProvider(_testOutputHelper);
+
+        var value = _fixture.Configuration!.GetValue<string>(Key);
+
+        Assert.Equal(Value, value);
+    }
+}

src/Abstracts/TestBedFixture.cs

@@ -23,8 +23,6 @@ protected TestBedFixture()
 	{
 		_services = new ServiceCollection();
 		ConfigurationBuilder = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory());
-		AddUserSecrets(ConfigurationBuilder);
-		Configuration = GetConfigurationRoot();
 		_servicesAdded = false;
 	}
 
@@ -51,6 +49,8 @@ public ServiceProvider GetServiceProvider(ITestOutputHelper testOutputHelper)
 		}
 		if (!_servicesAdded)
 		{
+			AddUserSecrets(ConfigurationBuilder);
+			Configuration = GetConfigurationRoot();
 			AddServices(_services, Configuration);
 			_services.AddLogging(loggingBuilder => AddLoggingProvider(loggingBuilder, new OutputLoggerProvider(testOutputHelper)));
 			_services.AddOptions();