Test process env with Jest

Question

I have an application that depends on environmental variables like  const APP PORT   process env APP PORT    8080   And I would like to test that for example   APP PORT can be set by a Node js environment variable  or that an Express js application is running on the port set with process env APP PORT  How can I achieve this with Jest  Can I set these process env variables before each test or should I mock it somehow maybe

User · Answer

Jest s setupFiles is the proper way to handle this  and you need not install dotenv  nor use an  env file at all  to make it work   jest config js   module exports       setupFiles     lt rootDir gt   jest setEnvVars js         jest setEnvVars js   process env MY CUSTOM TEST ENV VAR    foo    That s it

User · Answer

You can use the setupFiles feature of the Jest configuration  As the documentation said that   A list of paths to modules that run some code to configure or set up the testing environment  Each setupFile will be run once per test file  Since every test runs in its own environment  these scripts will be executed in the testing environment immediately before executing the test code itself    npm install dotenv dotenv that uses to access environment variable   Create your  env file to the root directory of your application and add this line into it    env APP PORT 8080   Create your custom module file as its name being someModuleForTest js and add this line into it     someModuleForTest js require  quot dotenv quot   config     Update your jest config js file like this  module exports       setupFiles    quot   someModuleForTest quot       You can access an environment variable within all test blocks  test  quot Some test name quot        gt      expect process env APP PORT  toBe  quot 8080 quot

User · Answer

In   package json    jest        setupFiles           lt rootDir gt  jest setEnvVars js          In   jest setEnvVars js   process env SOME VAR    value

User · Answer

Expanding a bit on Serhan C  s answer    According to the blog post How to Setup dotenv with Jest Testing - In-depth Explanation  you can include  quot dotenv config quot  directly in setupFiles  without having to create and reference an external script that calls require  quot dotenv quot   config    I e   simply do module exports         setupFiles    quot dotenv config quot

User · Answer

Depending on how you can organize your code  another option can be to put the environment variable within a function that s executed at runtime  In this file  the environment variable is set at import time and requires dynamic requires in order to test different environment variables  as described in this answer   const env   process env MY ENV VAR   const envMessage        gt   MY ENV VAR is set to   env      export default myModule   In this file  the environment variable is set at envMessage execution time  and you should be able to mutate process env directly in your tests  const envMessage        gt      const env   process env MY VAR    return  MY ENV VAR is set to   env        export default myModule   Jest test  const vals        ONE      TWO      THREE       vals forEach  val    gt      it  Returns the correct string for each   val  value        gt        process env MY VAR   val       expect envMessage    toEqual

User · Answer

Another option is to add it to the jest config js file after the module exports definition  process env   Object assign process env      VAR NAME   varValue     VAR NAME 2   varValue2       This way it s not necessary to define the environment variables in each  spec file and they can be adjusted globally

User · Answer

The way I did it can be found in this Stack  Overflow question  It is important to use resetModules before each test and then dynamically import the module inside the test  describe  environmental variables        gt      const OLD ENV   process env     beforeEach      gt        jest resetModules      Most important - it clears the cache     process env        OLD ENV       Make a copy          afterAll      gt        process env   OLD ENV     Restore old environment          test  will receive process env variables        gt           Set the variables     process env NODE ENV    dev       process env PROXY PREFIX     new-prefix        process env API URL    https   new-api com        process env APP PORT    7080       process env USE PROXY    false        const testedModule   require        config env   default             actual testing            If you look for a way to load environment values before running the Jest look for the answer below  You should use setupFiles for that

User · Answer

In my opinion  it s much cleaner and easier to understand if you extract the retrieval of environment variables into a utility  you probably want to include a check to fail fast if an environment variable is not set anyway   and then you can just mock the utility     util js exports getEnv    key    gt        const value   process env key       if  value     undefined          throw new Error  Missing required environment variable   key               return value         app test js const util   require    util    jest mock    util     util getEnv mockImplementation key   gt   fake-  key      test  test        gt

User · Answer

In test file  const APP PORT   process env APP PORT    8080   In the test script of   package json   quot scripts quot         quot test quot    quot jest --setupFiles dotenv config quot       In   env  APP PORT 8080

User · Answer

I think you could try this too    const currentEnv   process env  process env     ENV NODE   whatever         test code     process env   currentEnv    This works for me and you don t need module things

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