Assertions

The test section of a step asserts the response. Plain values are compared for equality, and the body is matched key by key, as deep as you write it:

test:
  status: 400
  body:
    error:
      code: DIVISION_BY_ZERO

A step without a test passes as long as the method does not fail.

JavaScript expressions

For anything beyond equality, prefix the value with $expr: and write JavaScript, where value is the actual value being tested:

test:
  body:
    count: "$expr: value > 10"
    items: "$expr: Array.isArray(value) && value.length >= 3"
    user:
      age: "$expr: value >= 18 && value <= 65"

Validation	Expression
Greater than	$expr: value > 0
Exact value	$expr: value === 2
In a range	$expr: value >= 5 && value <= 10
String contains	$expr: typeof value === 'string' && value.includes('ok')
Array has items	$expr: Array.isArray(value) && value.length > 0
Property exists	$expr: typeof value === 'object' && 'id' in value
Date after	$expr: new Date(value) > new Date('2023-01-01')

Random values are the usual reason to reach for an expression: a body that echoes {{ randomEmail }} cannot be compared to a literal, but it can be checked for shape.

Asserting against what an earlier step remembered

A test block is not templated: {{ memory.barcode }} written in one is compared as the twenty characters it is, not as the barcode. To assert against something an earlier step left behind, use an expression: memory is in scope beside value, and so is the whole flow.

test:
  body:
    barcode: "$expr: value === memory.barcode"
    data: "$expr: value.some(i => i.barcode === memory.barcode)"

How the memory gets written is in Passing data between steps.

Messages that arrive later

An effect that does not come back in the response, a message published on MQTT after the call, is asserted with test.latentApplications. See Latent applications.

Cover the unhappy paths

Asserting that a missing resource returns 404 is what catches the regression that starts answering 200. A flow that only checks success only ever fails when everything breaks.