What is an Assertion?

  • An API test consists of a series of steps (these are sometimes HTTP requests) that can be executed collectively or individually.
  • An assertion is a specification that indicates the expected outcome (response) to a request executed in a test.
  • A test is unsuccesful if an assertion fails i.e. the actual outcome is not equal to the expected outcome
  • You can create assertions for status codes, response time, reponse content, header values, etc.
  • When you execute an assertion, you can determine the type of operation you want to perform with your expected outcomes.

Comparison Logic Available in Scenarios

  • equals
  • greater than
  • greater than or equals
  • less than
  • less than or equals
  • no equal
  • exists
  • length equals
  • contains
  • validate pass
  • validate fail


  • Assertions are checked any time a test is executed.
  • Assertions are used to detemine the state of a test (pass or fail).
  • Assertions are ideal for discovering if an API satisfies stipulated objectives.

Assertions in Scenarios

  • Scenarios in Stoplight are grouped into collections. To create an assertion for a step in Scenarios, you need to create a collection and add your Scenarios to it.