Writing Custom Tests for Response Validation
Going Beyond Basic Checks
While status code and response time checks cover the basics, real APIs often need deeper validation - checking specific field values, data types, or business rules within the response.
Parsing the Response Body
Using pm.response.json(), a script can parse the response body into a JavaScript object and then assert on individual fields, nested objects, or array lengths.
Example Validation Patterns
| Pattern | Purpose |
|---|---|
| Field existence check | Confirms a key is present in the response |
| Data type check | Confirms a field is a string, number, etc. |
| Value range check | Confirms a number falls within limits |
| Array length check | Confirms a list has expected number of items |
Reusable Test Logic
Common validation logic can be stored as functions in collection-level scripts, so multiple requests can reuse the same custom checks without duplicating code.
Custom validation often means working closely with the response format itself - let's look at checking JSON and XML responses specifically.
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