Assertions

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

[assert]
status = 200

JSON body paths

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

Check response headers:

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

Response time

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 F# scripts

For assertions that go beyond the declarative syntax, use F# post-request scripts:

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

// validate-schema.fsx
let users = ctx.Response.Json.EnumerateArray() |> Seq.toList

for user in users do
    if not (user.TryGetProperty("email") |> fst) then
        ctx.Fail $"User {user.GetProperty("id")} missing email"