Rspec Expect to Receive: Demystifying the “not_to receive” Method

When it comes to testing in Rspec, one of the most powerful tools in your arsenal is the “expect to receive” method. But what happens when you want to test that a method is not called? That’s where the “not_to receive” method comes in. In this article, we’ll delve into the world of Rspec expect to receive, and explore how to use “not_to receive” to take your testing to the next level.

What is the “expect to receive” method?

Before we dive into “not_to receive”, let’s quickly cover the basics of “expect to receive”. The “expect to receive” method is used to set an expectation that a method will be called on an object. It’s a way to verify that a specific method is being called, and that it’s being called with the correct arguments.

expect(my_object).to receive(:my_method).with('arg1', 'arg2')

This code sets an expectation that the `my_method` method will be called on `my_object`, and that it will be called with the arguments `’arg1’` and `’arg2’`. If the method is not called, or if it’s called with different arguments, the test will fail.

Introducing “not_to receive”

Now that we have a solid understanding of “expect to receive”, let’s talk about its opposite: “not_to receive”. The “not_to receive” method is used to set an expectation that a method will not be called on an object.

expect(my_object).not_to receive(:my_method)

This code sets an expectation that the `my_method` method will not be called on `my_object`. If the method is called, the test will fail.

Why use “not_to receive”?

So why would you want to use “not_to receive”? There are a few scenarios where this method is particularly useful:

• You want to verify that a method is not being called unnecessarily. For example, you might have a method that sends an email, and you want to make sure it’s not being called unless it’s absolutely necessary.

• You want to test that a method is not being called with specific arguments. For example, you might have a method that processes a payment, and you want to make sure it’s not being called with a specific payment method.

• You want to verify that a method is not being called at all. For example, you might have a method that’s deprecated, and you want to make sure it’s not being used anywhere in your codebase.

Examples of “not_to receive” in action

Let’s take a look at some examples of “not_to receive” in action. Suppose we have a `User` class with a `send_email` method:

class User
  def send_email
    # send email logic here
  end
end

We can use “not_to receive” to verify that the `send_email` method is not called unless a specific condition is met:

it 'does not send an email if the user is not subscribed' do
  user = User.new(subscribed: false)
  expect(user).not_to receive(:send_email)
  user.do_something
end

In this example, we’re setting an expectation that the `send_email` method will not be called on the `user` object unless the user is subscribed. If the method is called, the test will fail.

Another example might be testing that a method is not called with specific arguments:

it 'does not process a payment with a specific payment method' do
  payment = Payment.new(payment_method: 'paypal')
  expect(payment).not_to receive(:process_payment).with('stripe')
  payment.do_something
end

In this example, we’re setting an expectation that the `process_payment` method will not be called on the `payment` object with the argument `’stripe’`. If the method is called with this argument, the test will fail.

Troubleshooting “not_to receive” issues

So what happens when your “not_to receive” test fails? There are a few common issues that might cause problems:

1. Method is being called unintentionally: Make sure that the method is not being called anywhere in your codebase. Use tools like RubyMine or IntelliJ to search for usages of the method.

2. Method is being called in a different context: Make sure that the method is not being called in a different context, such as in a different test or in a different part of the codebase.

3. Method is being called asynchronously: If the method is being called asynchronously, you might need to use a tool like `expect_async` to wait for the method to be called.

By following these tips, you should be able to track down and fix any issues with your “not_to receive” tests.

Conclusion

In conclusion, the “not_to receive” method is a powerful tool in Rspec that allows you to set an expectation that a method will not be called on an object. By using “not_to receive”, you can ensure that your code is following the expected behavior, and catch any unexpected method calls. Remember to use “not_to receive” judiciously, and to troubleshoot any issues that arise.

Method	Description
`expect(my_object).to receive(:my_method)`	Sets an expectation that `my_method` will be called on `my_object`
`expect(my_object).not_to receive(:my_method)`	Sets an expectation that `my_method` will not be called on `my_object`

By mastering “not_to receive”, you’ll be able to write more comprehensive and effective tests, and ensure that your code is behaving as expected.

Frequently Asked Question

RSpec’s `expect to receive` can be a bit tricky when it comes to testing that a method is not called. Here are some frequently asked questions about how to use it correctly: