rspec/rules/S5958/javascript/rule.adoc

It is not good enough to test if an exception is raised, without checking which exception it is. Such tests will not be able to differentiate the expected exception from an unexpected one. They should instead validate the exception message and/or type.

This rule raises an issue in the following cases:

* When an asynchronous Mocha test calls the ``++done()++`` callback, without parameters, in a ``++catch++`` block and there is no reference to the caught exception in this block. Either the error should be passed to ``++done()++`` or the exception should be checked further.
* When Chai assertions are used to test if a function throws any exception, or an exception of type ``++Error++`` without checking the message.
* When Chai assertions are used to test if a function does not throw an exception of type ``++Error++`` without checking the message.

== Noncompliant Code Example

----
const expect = require("chai").expect;
const fs = require("fs");

describe("exceptions are not tested properly", function() {
    const funcThrows = function () { throw new TypeError('What is this type?'); };
    const funcNoThrow = function () { /*noop*/ };

    it("forgot to pass the error to 'done()'", function(done) {
        fs.readFile("/etc/zshrc", 'utf8', function(err, data) {
            try {
                expect(data).to.match(/some expected string/);
            } catch (e) {  // Noncompliant
                // Either the exception should be passed to done(e), or the exception should be tested further.
                done();
            }
        });
    });

    it("does not 'expect' a specific exception", function() {
        expect(funcThrows).to.throw();  // Noncompliant
        // Error is not precise enough
        expect(funcThrows).to.throw(Error);  // Noncompliant
        expect(funcNoThrow).to.not.throw(Error);  // Noncompliant.
    });
});
----

== Compliant Solution

----
const expect = require("chai").expect;
const { AssertionError } = require('chai');
const fs = require("fs");

describe("exceptions are tested properly", function() {
    const funcThrows = function () { throw new TypeError('What is this type?'); };
    const funcNoThrow = function () { /*noop*/ };

    it("forgot to pass the error to 'done()'", function(done) {
        fs.readFile("/etc/zshrc", 'utf8', function(err, data) {
            try {
                expect(data).to.match(/some expected string/);
            } catch (e) {
                expect(e).to.be.an.instanceof(AssertionError);
                done();
            }
        });
    });

    it("does not 'expect' a specific exception", function() {
        expect(funcThrows).to.throw(TypeError);
        expect(funcNoThrow).to.not.throw(Error, /My error message/);
    });
});
----