mock-rest-apis

Mock REST APIs Skill

Use this skill when a REST integration needs an endpoint you control instead of a live third-party API — while building it, while reproducing a bug, or while verifying the app in a browser or a test run.

Developing against the real API means network, rate limits, credentials, and a payload that can change under you. None of that is where Mendix integration defects live: those are in the mapping, the entity types, the error handler, and the BSON. A mock removes the variables that are not the bug.

When to Use This Skill

• Building a REST client or REST CALL microflow before (or without) real credentials
• Reproducing a payload-shaped bug deterministically — a shape small enough to read, that behaves the same on every run
• Exercising error paths: 404, 500, a timeout, a 401 from missing auth
• Verifying the app (test-app) or running a suite (test-microflows) offline or in CI
• Redirecting the outbound calls of an app whose model you must not edit

Two separate problems

Almost every wasted hour here comes from conflating them:

Problem	Answer
Something must answer the request	A mock server: Prism (from a contract), WireMock, mitmproxy
The app must send the request there	A constant, a BaseUrl, or a forward proxy — see below

A mock server is not an interceptor. Prism serves one contract at one port and answers only clients that address it. Asking it to "catch all calls the app already makes" is a category error — that is the forward-proxy job, further down.

1. Point the app at the mock

Three routes, cheapest first. Pick by how the URL is built.

The URL is built in the microflow — use a constant, change nothing per run

A REST CALL URL is an expression, so it can be assembled from a constant (@Module.Constant is Mendix's constant reference — $Name is a variable):

create constant MyModule.ApiBaseUrl type String default 'https://api.example.com/v1';

create microflow MyModule.CallApi() returns string
begin
  $response = rest call get @MyModule.ApiBaseUrl + '/rates'
    header Accept = 'application/json'
    returns string;
  return $response;
end;