Hypothesist 2.0.16

Hypothesist

The future assertion library for .NET.

This library is there to help you do assertions on events that are about to happen in the near future. For example, when building integration tests for a subscriber on a service bus.

Define

Define your hypothesis with an experiment, time constraint and test:

var hypothesis = Hypothesis
    .For<Data>()
    .Any(x => x.Value == 1234);

Test

You test your hypothesis by providing samples:

await hypothesis.Test(sample);

For example with an injected stub:

var service = Substitute.For<IDemoService>();
service
    .When(x => x.Demo(Arg.Any<Data>()))
    .Do(x => hypothesis.Test(x.Arg<Data>()));

or with a hand-rolled implementation:

class TestService : IDemoService
{
    private readonly IHypothesis<Data> _hypothesis;

    public TestService(IHypothesis<Data> hypothesis) => 
        _hypothesis = hypothesis;

    public Task Demo(Data data) =>
        _hypothesis.Test(data);
}

var service = new TestService(hypothesis);

or with the consumer factory Hypothesist.MassTransit when using MassTransit:

cfg.ReceiveEndpoint("...", x =>
{
    x.Consumer(hypothesis.AsConsumer);
});

Validate

You validate if your hypothesis holds true for the supplied samples during the specified time window.

await hypothesis.Validate(15.Seconds()); // <-- using TimeSpan extension from FluentAssertions

But somewhere in between you've fired off the eventing mechanism that ultimately invokes the injected service.

Experiments

The two parts of the hypothesis are the experiment and a time constraint.

Any

Validates that at least one item matches the assertion, meaning the experiment stops when this item is observed.

All

Validates that all items that are observed during the experiment matches the assertion.

Remark: having no items observed during the time window also means the hypothesis holds true;

First

Validates that the first item that is observed matches the assertion.

Single

Validates that exactly one item is observed that matches the assertion.

Remark: having other items not matching the assert means the hypothesis still holds true.

Exactly

Validates that exactly the given number of occurrences is observed that matches the assertion within the given timeframe.

AtLeast

Validates that at least the given number of occurrences is observed that matches the assertion.