Writing test classes

Test frameworks like pytest and unittest don't allow custom __init__ methods in test classes. To inject dependencies into test classes, use LazyInstance for sync dependencies and aget_lazy_instance for async dependencies.

Using LazyInstance

The LazyInstance descriptor resolves dependencies on access:

from injection import LazyInstance


class TestFeature:
    dependency = LazyInstance(Dependency)

    def test_something(self):
        result = self.dependency.some_method()
        assert result == expected_value

Using aget_lazy_instance for async

For async dependencies, use aget_lazy_instance which returns an awaitable:

from injection import aget_lazy_instance


class TestAsyncFeature:
    lazy_dependency = aget_lazy_instance(AsyncDependency)

    async def test_something(self):
        dependency = await self.lazy_dependency
        result = await dependency.some_method()
        assert result == expected_value

Tip

Use LazyInstance for sync dependencies (cleaner syntax) and aget_lazy_instance only when you need async dependencies.

Warning

LazyInstance resolves the dependency on every access. With transient dependencies, you get a new instance each time. With singletons, you get the same instance.