Can you write unit tests if you don't actually write the code?

Question

For instance, I assume this is what SDETs do?

They don't actually write the functional code but they're able to write integration/unit tests, am i correct?

But can someone learn to read code and then start writing tests?

Answer 1

This is actually a good question. I have been at the same place when I was working only on Manual Testing. Here is how I experienced things when I transitioned to automation. To answer your question, yes someone can read code and start writing tests on it but you need to understand the code that you are going to test.

There are different types of testing methodologies that are used when testing an application. These tests are done in layers so that the application is properly tested. Here is how the layering looks like:

1) Unit testing: This part is usually written by developers. This is because they have written the code and know the functionalities of the code and is easier for them to write. I am an SDET and I have written unit tests. There was only one opportunity that presented itself and it was when we were refactoring our code and there was a lot of room to write Unit Tests. In unit tests, you test functions in isolation by giving it some values and verifying an expected value. This is not something an SDET does, but should be able to do if provided the chance.

2) Integration testing: This part is also usually written by developers but the definition of integration testing is a bit vague. It means testing multiple modules in isolation. This can be modules in backend or modules in frontend but not together. Frameworks that help achieve this are code level integration tests for the technology you are using. Like for Angular application, there are deep integration tests that test the HTML and CSS of a component and there are shallow integration tests that just test two component's logic together. This can be written by an SDET but is usually written by the developer.

3) API testing (contract based testing): Pact helps us achieve this. There are other tools like rest assured, postman and jmeter that help in testing API end points. Pact helps test the integration of APIs on the frontend and verifies that integration in backend. This is very popular with microservices. This is something that can be written either by the developer or by the SDET.

4) End to End testing: This is something that is the sole responsibility of SDET. This covers testing of user flows depending on user stories. It is testing the entire stack together. Backend and frontend. This allows SDETs to automate how a user would use the application. This is also called as blackbox testing. There are different frameworks that help achieve this. Selenium, Protractor, Cypress, Detox etc. This is the sole responsibility of an SDET.

5) Load testing: This is again something that an SDET does. Using tools like hey, jmeter, loadrunner etc. These tests allow the SDET to initiate a heavy load on the system and check for breaking points of the system.

6) Performance testing: Testing the performance of the webpage for an end user depending on the page load time, the SEO optimisation and the weight of elements of page. This is something achieved by google's lighthouse tool that is an amazing tool to use. I am not aware of anything else that is as amazing as lighthouse because it gives us a lot of data that we can use to improve our website. This is a primary job of an SDET.

7) CI/CD: Continuous Integration and Continuous Deployments is something that requires architectural knowledge of the system. This is something you can do when you are an SDET3 or a lead QA engineer. For systems like AWS and GCP, using CI build tools like Jenkins and CircleCI, one can set up a pipeline that runs all the above tests when ever a branch is merged into master or whenever a pull request is created. Creating the pipeline will require you to have knowledge of Docker, Kubernetes, Jenkins and your test frameworks. First you dockerize your tests, then you build the image and push it to a directory in cloud, then you use the image to create a kubernetes job that runs everytime a change is presented in your code.

These are the levels of work that an SDET does. It takes time and hard work to have an understanding of all testing frameworks and how everything fits together. An SDET should have knowledge of the server, http protocols, frontend, backend, browsers, caching, pipeline management and orchestration of tests.

Answer 2

Yes, sure. You can write unit tests increasing test coverage of the codebase. That's very qualified work from software test engineering since you need to be aware what is going on in the code. This skill is definitely great!

I advise you to take a look on so called "mutation coverage". Usage of mutation coverage as a better metric than simple unit test coverage. Mutation tests are changing logical operators in the different parts of the codebase (making so called "mutants") and then are running unit tests to find out how many unit tests will fail showing their effectiveness (if after mutants were injected the result is the same as without them - unit tests quality is low and they won't catch any new injected issues to the codebase).