Mocking dates

A project created to test date mocking in applications running in docker containers. The project uses the libfaketime library which intercepts various system calls that programs use to retrieve the current date and time.

A description of how the Node.js example works

1. I created a custom docker image where I installed the libfaketime library and created a .faketimerc file which is used to set the date.
2. I have configured the api service in the docker-compose.yml file where I declared that the date should be taken from the /home/node/.faketimerc file located in the docker container.
3. During automated tests, I change the content of the /home/node/.faketimerc file by which the date that the new Date() call returns changes.

A description of how the PostgreSQL example works

1. I created a custom docker image where I installed the libfaketime library.
2. I have configured the database service in the docker-compose.yml file where I declared that the date should be taken from the FAKETIME environment variable declared in the docker container.
3. During automated tests, I run the SELECT NOW(); query to return the date that PostgreSQL server sees.

A description of how the Redis example works

1. I created a custom docker image where I installed the libfaketime library.
2. I have configured the cache service in the docker-compose.yml file where I declared that the date should be taken from the /home/node/.faketimerc file located in the docker container.
3. During automated tests, I run the queries against redis cache and validate that the cache is being correctly cleared and set.

Running tests

In order to test how the library works, I wrote automated tests in the src/app.controller.spec.ts file. To run the tests follow these steps:

1. Start the docker containers via the yarn up command.
2. Connect to the terminal in the container running the Node.js application via the yarn shell command.
3. Run automated tests via the yarn test command.

Conclusion

• Mocking dates in Node.js doesn't seem like the best solution to me. It works, but causes the test runner Jest to show incorrect test execution time results (e.g. -720000 seconds). I think that for mocking dates in Node.js it would be better to use the mockdate library, as it does not affect the behavior of Jest and is simpler to set up.
• Mocking dates in PostgreSQL seems to work without problems and can be a good solution if we want to test SQL queries that use time functions (e.g. NOW()).
• Mocking dates in Redis seems to work without problems and can be a good solution if we want to test the application that manages the cache.

Resources

• The libfaketime project repository on GitHub.