expect() with no actual expectations

Question

The Problem:

Recently, while reviewing our existing test codebase, I've noticed a dangerous kind of typo/mistake when expect() was used without the "matching" part:

expect(page.filters.fromDateLabel.getText(), "After");

I'm pretty sure toEqual() was meant to be used here:

expect(page.filters.fromDateLabel.getText()).toEqual("After");

The problem with this is that jasmine would not fail the expectation in this case (well, obviously because nothing was actually expected). And this gets us to a more serious problem - nothing was actually tested in a test case - it was passing with no expectations made. We were getting a false sense of what was tested.

The Question:

I want to catch these mistakes as fast as possible. How do you think I should handle the problem?

Thoughts:

• somehow fail a test case if there was no expectations made in it (not sure if jasmine has anything like this built-in)
• "patch" the expect() and issue a warning/raise an error if nothing was called on the "expect" part
• use static code analysis - define a custom eslint rule

Answer 1

The custom ESLint rule provided in the answer is now a part of eslint-plugin-jasmine 1.6.0:

• valid-expect

---

Old Answer:

Here is a custom ESLint rule I've ended up with:

module.exports = function (context) {
  return {
    // checking "expect()" arguments
    CallExpression: function (node) {
      if (node.callee.name === 'expect') {
        if (node.arguments.length > 1) {
          context.report(node, 'More than one argument passed to expect()')
        } else if (node.arguments.length === 0) {
          context.report(node, 'No arguments passed to expect()')
        }
      }
    },

    // nothing called on "expect()"
    'CallExpression:exit': function (node) {
      if (node.callee.name === 'expect' && node.parent.type === 'ExpressionStatement') {
        context.report(node, 'Nothing called on expect()')
      }
    }
  }
}

It checks for 3 things:

• more than 1 argument passed to expect()
• no arguments are passed to expect()
• there was nothing called on expect()

Here are the sample invalid expect() usages it currently catches:

expect(page.filters.fromDateLabel.getText(), "After");
expect("After");
expect();

---

As for the option #1, there is actually a quite related and useful ESLint rule being already implemented and open-sourced by [eslint-plugin-jasmine]:

• Enforce expectation (missing-expect)