Write tests that exercise functionality the same way a real consumer would, and make sure asynchronous tests fail loudly rather than hanging. Prefer wiring behavior through the public API inside a request handler and asserting with supertest’s request(app).get('/').expect(...), instead of calling internal methods directly, testing an unrelated helper function, or constructing ad-hoc objects that don’t match how the library is actually used:
// Bad: tests an internal helper, not the actual behavior change
assert.throws(typeThrowError(name), TypeError)
// Good: exercises the change through the public API
it('should raise error for invalid status code', function (done) {
var app = express()
app.use(function (req, res) {
res.sendStatus(1000)
})
request(app)
.get('/')
.expect(500, /Invalid status code/, done)
})
For async tests, always call done() on every path and guard assertions made inside callbacks with try/finally (or let them propagate) so a regression surfaces as a normal failure instead of a timeout:
var server = app.listen(0, function () {
try {
assert.throws(function () {
server.emit('error', new Error('boom'))
})
} finally {
server.close(done)
}
})
Avoid flakiness from hardcoded resources: use dynamic/ephemeral ports (listen(0)) instead of fixed port numbers that can collide across parallel runs, and size timeouts to tolerate slower CI/hardware rather than assuming a fast default. Keep new tests in the suite that matches the method under test (e.g. don’t add res.status assertions inside res.sendStatus tests), and use the project’s standard assertion library (assert.strictEqual, assert.deepEqual, assert.throws, or supertest’s .expect()) instead of manual if/else checks or legacy libraries like should that mutate global prototypes.