The done callback is used to inform Mocha when an asynchronous test ends. Exceptions thrown after done (with or without
parameters) is called are not handled in a consistent manner. Sometimes they will be correctly handled, but they might as well be assigned to a
different test, no test at all, or even be completely ignored. Even when it works as expected this will be a source of confusion for other developers.
Thus no code should be executed after done is called.
This rule raises an issue when some code is executed after a call to done.
Noncompliant Code Example
const expect = require("chai").expect;
const fs = require("fs");
describe("Code is executed after Done", function() {
it("Has asserts after done()", function(done) {
try {
expect(1).toEqual(2);
} catch (err) {
done();
// This assertion will be ignored and the test will pass.
expect(err).to.be.an.instanceof(RangeError); // Noncompliant
}
});
it("Throws an error some time after done()", function(done) {
fs.readFile("/etc/bashrc", 'utf8', function(err, data) {
done();
setTimeout(() => { // Noncompliant
// This assertion error will not be assigned to any test.
// Developers will have to guess which test failed.
expect(data).to.match(/some expected string/);
}, 3000);
});
});
it("Has code after done(err)", function(done) {
try {
throw Error("An error");
} catch (err) {
done(err);
}
fs.readFile("/etc/bashrc", 'utf8', function(err, data) { // Noncompliant
// This assertion error will be assigned to "Other test".
expect(data).to.match(/some expected string/);
});
});
it("Other test", function(done) {
done()
});
});
Compliant Solution
const expect = require("chai").expect;
const fs = require("fs");
describe("Code is executed after Done", function() {
it("Has asserts after done()", function(done) {
try {
expect(1).toEqual(2);
} catch (err) {
expect(err).to.be.an.instanceof(RangeError);
done();
}
});
it("Throws an error some time after done()", function(done) {
fs.readFile("/etc/bashrc", 'utf8', function(err, data) {
setTimeout(() => {
expect(data).to.match(/some expected string/);
done();
}, 3000);
});
});
it("Has code after done(err)", function(done) {
try {
throw Error("An error");
} catch (err) {
return done(err);
}
fs.readFile("/etc/bashrc", 'utf8', function(err, data) {
// This assertion error will be assigned to "Other test".
expect(data).to.match(/some expected string/);
done();
});
});
it("Other test", function(done) {
done()
});
});
