no-comparison-or-assignment-inside-ok

This rule prevents two misuses of the ok() test framework function.

Assignments

The first is one where people accidentally put assignments into ok, like so:

ok(foo = bar, "Foo should be equal to bar");

This is similar to the builtin eslint rule no-cond-assign.

There is no autofix as the linter cannot tell if the assignment was intentional and should be moved out of the ok() call, or if it was intended to be some kind of binary comparison expression (and if so, with what operator).

Comparisons

The second is a stylistic/legibility/debuggability preference, where the linter encourages use of the dedicated Assert framework comparison functions. For more details on Assert, see Assert module.

This rule is autofixed, and will correct incorrect examples such as the following:

Examples of incorrect code for this rule:

ok(foo == bar);
ok(foo < bar);
ok(foo !== bar);

to something like:

Examples of correct code for this rule:

Assert.equal(foo, bar);
Assert.less(foo, bar);
Assert.notStrictEqual(foo, bar);

Rationale

There are a few reasons the more verbose form is preferable:

• On failure, the framework will log both values rather than just one, making it much easier to debug failing tests without having to manually add logging, push to try, and then potentially retrigger to reproduce intermittents etc.

• The Assert module is standardized and more widely understood than the old mocha/mochikit forms.

• It is harder to make typos like the assignment case above, and accidentally end up with tests that assert non-sensical things.

• Subjectively, when an additional message is long enough to cause prettier to split the statement across multiple lines, this makes it easier to see what the two operands of the comparison are.