AssertStep

An AssertStep can be understood as the following function ScenarioContext => Assertion. Its goal is to describe an expectation.

The test engine is responsible to test the validity of the provided Assertion which can be one of the following:

Equality assertions : test the equality of two objects using the cats Equals typeclass.
- GenericEqualityAssertion to leave all the details to Cornichon
```
When I AssertStep("always true!", _ => GenericEqualityAssertion(true, true))
```
- CustomMessageEqualityAssertion to provide a custom error message
```
CustomMessageAssertion[A](expected: A, result: A, customMessage: () ⇒ String)
```
Ordering assertions : compare two objects using the cats Order typeclass.
- GreaterThanAssertion
- LessThanAssertion
- BetweenAssertion
Collection assertions : test the state of a collection of elements
- CollectionEmptyAssertion
- CollectionNotEmptyAssertion
- CollectionSizeAssertion
- CollectionContainsAssertion
String assertion : assert the content of a given String value
- StringContainsAssertion
- RegexAssertion

Below is a longer example showing how to integrate an assertion into a scenario.

When I EffectStep.fromSync(
  title = "estimate PI",
  action = scenarioContext => scenarioContext.session.add("result", piComputation())
)

Then assert AssertStep(
  title = "check estimate",
  action = scenarioContext => Assertion.either{
    scenarioContext.session.get("result").map(r => BetweenAssertion(3.1, r.toDouble, 3.2))
  }
)

Assertions can also be composed using and and or, for instance BetweenAssertion is the result of LessThanAssertion and GreaterThanAssertion.

This is rather low level therefore you should not write your steps like that directly inside the DSL but hide them behind functions with appropriate names.

Fortunately a bunch of built-in steps and primitive building blocks are already available for you.

Note for advance users: it is also possible to write custom wrapper steps by implementing WrapperStep.