Implicit vs Explicit Modes

How ImposterMode affects methods, properties, and indexers when no setup exists.

Methods

Target type used in examples:

Example

using Imposter.Abstractions;

[assembly: GenerateImposter(typeof(IMyService))]

public interface IMyService
{
    int GetNumber();
    System.Threading.Tasks.Task<int> GetNumberAsync();
}

Implicit mode (methods)

Methods without setups are implicitly stubbed and return default(T).

Example

var imposter = new IMyServiceImposter(ImposterMode.Implicit);
var service = imposter.Instance();

// Method without a setup => default(int) == 0
int n = service.GetNumber(); // 0

// Add a setup and the call returns your value
imposter.GetNumber().Returns(42);
service.GetNumber(); // 42

// Async methods
imposter.GetNumberAsync().ReturnsAsync(7);
var v = await service.GetNumberAsync(); // 7

Explicit mode (methods)

Missing setups throw an exception so unintended calls are caught.

Example

var imposter = new IMyServiceImposter(ImposterMode.Explicit);
var service = imposter.Instance();

// No setup -> throws MissingImposterException
Should.Throw<MissingImposterException>(() => service.GetNumber());

// Add a setup -> call succeeds
imposter.GetNumber().Returns(42);
service.GetNumber(); // 42

Pro tip

Default to Explicit in unit tests to catch missing setups early. Use Implicit in spike/prototyping code where default results are acceptable.

Properties

In Implicit mode, property getters without setups return default(T) and setters do nothing. In Explicit mode, missing setups throw MissingImposterException.

Example

var imposter = new IPropertySetupSutImposter(ImposterMode.Implicit);
var sut = imposter.Instance();

// No getter setup => default(int) == 0
int n = sut.Age; // 0

// No setter setup => call is ignored
sut.Age = 10;

Example

var imposter = new IPropertySetupSutImposter(ImposterMode.Explicit);
var sut = imposter.Instance();

// No getter setup -> MissingImposterException
// sut.Age; // throws

// No setter setup -> MissingImposterException
// sut.Age = 10; // throws

Indexers

Indexers follow the same rules: Implicit mode returns defaults / does nothing; Explicit mode throws when no setup matches.

Example

var imposter = new IIndexerSetupSutImposter(ImposterMode.Implicit);
var sut = imposter.Instance();

// No setup => default(int) == 0
int value = sut[1, "key"]; // 0

// Setter without setup is ignored
sut[1, "key"] = 10;

Example

var imposter = new IIndexerSetupSutImposter(ImposterMode.Explicit);
var sut = imposter.Instance();

// No getter setup -> MissingImposterException
// var value = sut[1, "missing"]; // throws

// No setter setup -> MissingImposterException
// sut[1, "missing"] = 10; // throws