generic-testing.md

Generic testing

GenericTester (package UnitTestEx) runs any code inside a lightweight .NET Generic Host. You get UnitTestEx's DI, configuration, logging capture, expectations and assertions without needing an API or Function. Use it for domain services, repositories, message handlers and other plain classes.

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Create

using var test = GenericTester.Create();               // Empty host; only test configuration and logging.
using var test = GenericTester.Create<EntryPoint>();   // Host configured by an entry point class.

The entry point is any class that has one or more of the following methods. Each can be static or an instance method, and they're found by name using reflection, so no interface is needed:

Method	Purpose
ConfigureApplication(IHostApplicationBuilder builder)	Preferred; matches the modern Host.CreateApplicationBuilder style.
ConfigureServices(IServiceCollection services)	Service registrations.
ConfigureAppConfiguration(HostBuilderContext context, IConfigurationBuilder config)	App configuration.
ConfigureHostConfiguration(IConfigurationBuilder config)	Host configuration.

Example: Run_Service with its EntryPoint class.

new GenericTester<TEntryPoint, TValue>() gives the tester a value type, so ExpectValue is strongly typed.

Run

Run accepts a function or action, either sync or async (Task, ValueTask). The Run<TService> / Run<TService, TValue> overloads resolve TService from the host for you:

test.Run(() => 1).AssertSuccess().AssertValue(1);
test.Run<Gin, int>(gin => gin.Pour()).AssertValue(1);
test.Run<Gin>(gin => gin.Stir()).AssertException<DivideByZeroException>("As required by Bond; shaken, not stirred.");

Example: Run_Success, Run_Exception, Run_Service.

Run<TService> resolves from the root provider, so a scoped service throws Cannot resolve scoped service from root provider. Use ScopedType<TService> instead (see below).

Type<T> and ScopedType<T>

These are available on every tester (API, Function, Generic), so you can test any service registered in the host under test.

• Type<TService>() resolves the service from DI. If it isn't registered, it is constructed instead, with each constructor parameter resolved from DI. Then it runs methods on it.
• ScopedType<TService>(t => ...) creates a DI scope, resolves the service inside it, runs your test actions, then disposes the scope. Use this for scoped services, such as a DbContext or anything that depends on request-scoped state. UseScopedTypeSetUp(sp => ...) runs arrangement code inside every such scope first.

Example: ScopedType_RunsWithinServiceScope, Type_IActionResult.

Base classes

To reuse one tester across a whole fixture, inherit from the base class for your framework. It creates the tester once and exposes it as Test:

Framework	API	Generic
NUnit	WithApiTester<TEntryPoint>	WithGenericTester<TEntryPoint>
MSTest	WithApiTester<TEntryPoint>	WithGenericTester<TEntryPoint>
xUnit	WithApiTester<TEntryPoint> (with ApiTestFixture<TEntryPoint>)	UnitTestBase + GenericTester.Create<TEntryPoint>()

Example: Run_Success_AssertJSON.

See also: Dependency injection and configuration, Assertions and expectations.

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