fetcherino
A light-weight mocking tool for replacing fetch in your tests
Installation
npm i fetcherino --save-devMain advantages
- Lightweight and standalone: can be used out of the box with no external dependencies
- Can be seamlessy integrated into any environment: browser,
JSDOM,node-fetch - Clearcut API: single
fetch.mock(path, {request, response})method, no magic method chains - Clearcut behaviour: explicit request ordering, no "forever mocks", one-to-one mock-request correlation
- Informative errors: you'll know right away why your request didn't match existing mocks
Currently NOT supported
- Body streams
- AbortController
Example Usage
Note: any properties on the Response object in the examples below are only shown for demonstration purposes, you'd still have extract them according to fetch specification(e.g through async methods)
import { buildFetch } from "fetcherino";
let fetch = buildFetch();
let params;
// Each mock can only be consumed once
fetch.mock('/test');
fetch("/test").then(console.log); // => Response { status: 200, text: '' }
fetch("/test").catch(console.log); // => Unexpected fetch: GET /test
// Responses are returned in the order they were defined
fetch.mock('/test', { response: { body: 'Hello' } });
fetch.mock('/test', { response: { body: 'Hi' } });
fetch("/test").then(console.log); // => Response { status: 200, text: 'Hello' }
fetch("/test").then(console.log); // => Response { status: 200, text: 'Hi' }
// Objects are matched partially by default
fetch.mock('/test', { request: { body: { foo: 'bar' }, query: { a: 'b' } } });
params = {
method: 'POST',
body: JSON.stringify({foo: 'bar', bar: 'baz'}),
headers: { 'Content-Type': 'application/json' }
};
fetch("/test?a=b&b=c", params).then(console.log); // => Response { status: 200 }
// Pre-made and custom matchers
import { arrayIncluding } from 'fetcherino/matchers';
fetch.mock(
url => url.includes('test'),
{ request: { body: arrayIncluding(1) } }
);
params = {
method: 'POST',
body: JSON.stringify([1, 2, 3]),
headers: { 'Content-Type': 'application/json' }
}
fetch("/foobar/test/123", params).then(console.log); // => Response { status: 200 }
// Validating and resetting mocks
fetch.validateAndResetMocks(); // => does nothing since there are no mocks defined yet
fetch.mock('/test');
fetch.validateAndResetMocks(); // => Throws Not all fetch.mock request expectations were met
fetch("/test").catch(console.log); // => Unexpected fetch: GET /test
// JSDOM integration
import { JSDOM } from 'jsdom';
let jsdom = new JSDOM('<!doctype html><html><body></body></html>', { url: 'https://example.com' });
let { FormData, File } = jsdom.window;
let myFile = new File(['test'], 'foobar.pdf');
fetch.mock('/test', { request: { body: { foo: 'bar', file: myFile } } });
let fd = new FormData();
fd.append('foo', 'bar');
fd.append('file', myFile);
fetch('/test', {method: 'POST', body: fd}).then(console.log) // => Response { status: 200 };
buildFetch()
Returns a fetch function which will reject any unexpected request(i.e a request without defined matching mocks), but behaves like normal fetch otherwise.
Note: fetcherino does not by itself provide any functionality for mocking or replacing fetch globally. Each function returned from buildFetch is self-contained and does not share anything with other buildFetch() instances. If you want to have single global fetch function, you'll have to setup one yourself, for example:
// test_setup.js
import { buildFetch } from "fetcherino";
let fetch = buildFetch();
window.fetch = fetch;
global.fetch = fetch;
fetch.mock(urlMatcher, { request, response })
Allows you to define a request expectation for given url. For more details on matching requests see below.
Accepted request matchers: cache, credentials, mode, redirect, referrer, method, body, headers, query
Accepted response details: body, statusText, status, headers
fetch.validateAndResetMocks()
Resets all defined mocks for given fetch function. Will throw if there are unmatched(unconsumed) mocks left.
Matchers
Fetcherino implements potent but extremely simple and straightforward system for matching request expectations. Any request expectation detail passed to fetch.mock()(e.g url, request.body, request.headers) is converted into a matcher function according to the given expectation detail's type:
-
Functiondetails are returned as is. -
Objectdetails are converted into anobjectIncludingmatcher. - Anything else is converted into an
equalTomatcher.
Matcher function is any function which takes one argument and returns a boolean. For example, we can use a custom matcher function for the request url instead of passing it as a string:
import { buildFetch } from "fetcherino";
let fetch = buildFetch();
fetch.mock(url => url.includes('/test'));
// Error: Unexpected fetch: GET /foo
// Closest expectation: ANY function (url) {
// return url.includes(/test);
// }
fetch("/foo").catch(console.log);
// Response { status: 200 }
fetch("/test").then(console.log);
createMatcher(matcherFunction, description)
In the above example we dont have a good way of inspecting the expected url other than inspecting the matcher function itself. This is where the createMatcher helper comes in, allowing you to specify readable description for a matcher function:
import { buildFetch } from "fetcherino";
import { createMatcher } from "fetcherino/matchers";
let fetch = buildFetch();
fetch.mock(createMatcher(url => url.includes('/test'), "(url matching /test)"));
// Throws:
// Error: Unexpected fetch: GET /foo
// Closest expectation: ANY (url matching /test)
fetch("/foo").catch(console.log);
objectIncluding(subset)
Uses lodash.ismatch to match target object(e.g request body) against its potential subset. All objects given to fetch.mock are converted to this matcher by default.
import { buildFetch } from "fetcherino";
import { objectIncluding } from "fetcherino/matchers";
let fetch = buildFetch();
fetch.mock('/test', { request: { query: objectIncluding({foo: 'bar'}) } });
fetch('/test?foo=baz').catch(console.log); // Error: Unexpected fetch
fetch('/test?foo=bar&bar=baz').then(console.log); // Response { status: 200 }
equalTo(target)
Uses lodash.isequal to check two objects for equality. All strings, numbers, boolean arguments, etc., given to fetch.mock are converted to this matcher by default.
import { buildFetch } from "fetcherino";
import { equalTo } from "fetcherino/matchers";
let fetch = buildFetch();
fetch.mock('/test', { request: { query: equalTo({foo: 'bar'}) } });
fetch('/test?foo=bar&bar=baz').catch(console.log); // Error: Unexpected fetch
fetch('/test?foo=bar').then(console.log); // Response { status: 200 }
arrayIncluding(object)
Checks whether target array contains given object. Object equality is checked via lodash.isequal
import { buildFetch } from "fetcherino";
import { arrayIncluding } from "fetcherino/matchers";
let fetch = buildFetch();
function postJSON({body}) {
return {
body: JSON.stringify(body),
method: "POST",
headers: { 'Content-Type': 'application/json' }
};
}
fetch.mock('/test', { request: { body: arrayIncluding(1) } });
fetch('/test', postJSON({ body: [2, 3, 4] })).catch(console.log); // Error: Unexpected fetch
fetch('/test', postJSON({ body: [1, 2, 3] })).then(console.log); // // Response { status: 200 }
arrayIncludingSubset(subset)
Checks whether target array contains a superset of a given subset. Uses lodash.ismatch
import { buildFetch } from "fetcherino";
import { arrayIncludingSubset } from "fetcherino/matchers";
let fetch = buildFetch();
function postJSON({body}) {
return {
body: JSON.stringify(body),
method: "POST",
headers: { 'Content-Type': 'application/json' }
};
}
fetch.mock('/test', { request: { body: arrayIncludingSubset({a: 1}) } });
// Error: Unexpected fetch
fetch('/test', postJSON({ body: [1, 2, { a: 2 }] })).catch(console.log);
// Response { status: 200 }
fetch('/test', postJSON({ body: [1, 2, { a: 1, b: 2}] })).then(console.log);License
MIT