Borislav Hadzhiev
Sun Mar 13 2022·2 min read
Photo by Chuttersnap
To solve the "Cannot find name 'it'" jest error, make sure to install the
typings for jest - npm i -D @types/jest
and add them to the types
array in
your tsconfig.json
file. TypeScript has to be picking up the directory in
which your tests are located.
Here is an example of how the error occurs.
// Cannot find name 'it'. Do you need to install // type definitions for a test runner? Try // `npm i --save-dev @types/jest` or // `npm i --save-dev @types/mocha` and then add // 'jest' or 'mocha' to the types field in your tsconfig.ts(2593) describe('example', () => { it('does work', () => { expect('hello').toBe('hello'); }); });
Open your terminal in the root directory of your project and install the typings
for jest
.
npm i -D @types/jest ts-jest jest
Once the typings are installed, you have to add them to the types
array in
your tsconfig.json
file.
This should be what your types
array looks like.
{ "compilerOptions": { "types": [ "reflect-metadata", "jest", // ... your other types ], // ... your other settings } }
If the error is still not resolved, make sure that TypeScript is picking up the
directory in which your tests are located. If you've set the include
array in
your tsconfig.json
file, it should also include the directory in which your
tests are.
For example, if your tests are in an src
directory, the following config is
fine:
{ "compilerOptions": {}, "include": ["src/**/*"], }
However, if your tests are in a tests
directory next to your src
directory,
TypeScript won't pick them up with the config above.
{ "compilerOptions": {}, "include": [ "src/**/*", "tests/**/*" ], }
You can also use glob patterns. Here is an example that includes files ending in
.spec.ts
and .test.ts
.
{ "compilerOptions": {}, "include": [ "src/**/*", "**/*.spec.ts", "**/*.test.ts" ], }
The example above makes sure to also include your test files in your project. If you need a way to exclude your test files from compilation, but still have them type checked, check out my other article - Exclude test files from Compilation in TypeScript.
If the error persists and your runtime is Node.js, make sure to install the typings for node, by opening your terminal in your project's root directory and running the following command:
npm i -D @types/node
Also if running your code using Node.js, make sure the types
array in your
tsconfig.json
file contains "node"
.
{ "compilerOptions": { "types": [ // ... your other types "node" ], }, }
If the error is not resolved, try to delete your node_modules
and
package-lock.json
files, re-run npm install
and restart your IDE.
rm -rf node_modules package-lock.json npm install
Make sure to restart your IDE if the error still persists. VSCode glitches often and a reboot solves things sometimes.