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Documentation Index

Fetch the complete documentation index at: https://mintlify.com/michael-tiger-2010/wyvernjs/llms.txt

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FireWyrm provides lightweight object method mocking via fw.mock(). It replaces a named property on any object with a stub function, records the original value internally, and lets you restore everything in one call when the tests are finished. Mocking is useful for intercepting network calls, neutralising side-effectful functions like console.log, or making timers and other browser APIs behave predictably during a test run — all without any external library.

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fw.mock(fn)

Creates a mock descriptor. fn is the replacement function to install. If fn is omitted, a no-op (() => {}) is used. Returns an object with a single method: .replace(obj, prop).

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.replace(obj, prop)

Swaps obj[prop] for the stub function supplied to fw.mock(). The original value is saved so it can be restored later. Returns the internal mock record (not fw) — further chaining is not typical here. 
// Replace window.fetchJson with a stub that resolves immediately
fw.mock(() => Promise.resolve({ data: 1 })).replace(window, 'fetchJson');

// Silence console.log during a noisy test (no-op replacement)
fw.mock().replace(console, 'log');

// Replace with a custom spy
let callCount = 0;
fw.mock(() => callCount++).replace(myModule, 'trackEvent');

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fw.mock.restore(select?)

Restores mocked properties to their original values. By default it restores all active mocks. Pass a property name string to restore only that specific replacement. 
fw.mock.restore();             // restore every mock
fw.mock.restore('fetchJson');  // restore only the fetchJson mock
After restore() is called, the internal mocks list is cleared.

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Full example

The pattern below shows the complete lifecycle: mock before the tests that depend on it, run the tests, then restore everything inside the fw.end() callback. 
fw.start();

// Install mock before the section that needs it
fw.mock(() => Promise.resolve({ user: 'alice', role: 'admin' }))
  .replace(window, 'fetchJson');

fw.section('User API (mocked)');
fw.test('Returns user data', async () => {
  const data = await fetchJson('/api/user');
  return data.user === 'alice';
});
fw.assert('Role is admin', async () => {
  const data = await fetchJson('/api/user');
  return data.role;
}).is('admin');

// Restore all mocks once the run is done
fw.end().then(() => {
  fw.mock.restore();
});
Always call fw.mock.restore() after your tests complete. Leaving mocks in place will affect any other code that runs afterwards — including other test files or live application logic if you are running FireWyrm in the same browser page as your app.
FireWyrm mocking is intentionally minimal — it replaces properties on existing objects, not module-level imports. If you need to intercept ES module imports (e.g. import { fetchJson } from './api.js') in a bundler environment, use your bundler’s own mock facilities (such as Vite’s vi.mock() or webpack’s jest.mock()) alongside FireWyrm’s assertion layer.

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