Assertions (spec: nap-assert)

The [assert] section in .nap files provides declarative assertions on HTTP responses. No scripting needed for common checks.

Syntax

Each assertion is a single line in the form:

target operator value

Status code (spec: assert-status)

[assert]
status = 200

JSON body paths (spec: assert-equals, assert-exists, assert-gt)

Assert on values in the JSON response body using dot notation:

[assert]
body.id = 1
body.name = "Ada Lovelace"
body.email exists
body.users.length > 0

Headers (spec: assert-contains, assert-exists)

Check response headers:

[assert]
headers.Content-Type contains "application/json"
headers.X-Request-Id exists

Response time (spec: assert-lt)

Assert that the response completes within a time limit:

[assert]
duration < 500ms
duration < 2s

Operators

Multiple assertions

Add as many assertions as you need:

[assert]
status = 200
body.id exists
body.name = "Ada Lovelace"
body.email contains "@"
headers.Content-Type contains "application/json"
duration < 1000ms

All assertions are evaluated. Napper reports each one as passed or failed.

Complex assertions with scripts

For checks that go beyond the declarative syntax, use a JavaScript or Python post-request hook. The injected ctx object gives you the parsed response, and ctx.fail(message) fails the request:

[script]
post = ./scripts/validate-schema.js

// validate-schema.js — ctx is a global, no import
for (const user of ctx.response.json) {
  if (!user.email) ctx.fail("user " + user.id + " is missing email");
}

F# and C# scripts can also run as post hooks, but they validate by exit code rather than the ctx object — see the F# and C# guides.