Cannot find name 'it' or 'describe' error in TypeScript

# Cannot find name 'it' or 'describe' Error in TypeScript

To solve the "Cannot find name 'describe'" error, install the type definitions for your test runner, e.g. npm i -D @types/jest or npm i -D @types/jasmine and make sure to add the typings for the package in the types array in your tsconfig.json file.

Here is an example of how the error occurs.

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// ⛔️ Error: Cannot find name 'describe'. 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('multiplies two numbers', () => {
    expect(5 * 5).toBe(25);
  });
});

# Install the typings for your test runner

Open your terminal in the root directory of your project and install the typings for your test runner. Here are the comments for jest, mocha and jasmine.

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# ✅ with NPM

# 👇️ Jest
npm i -D @types/jest ts-jest jest

# 👇️ Mocha
npm i -D @types/mocha mocha

# 👇️ Jasmine
npm i -D @types/jasmine jasmine

# -----------------------------

# ✅ with YARN

# 👇️ Jest
yarn add --dev @types/jest jest

# 👇️ Mocha
yarn add --dev @types/mocha mocha

# 👇️ Jasmine
yarn add --dev @types/jasmine jasmine

# Add the typings to the types array in tsconfig.json

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 if you use the jest test runner.

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{
  "compilerOptions": {
    "types": [
      "reflect-metadata",
      "jest",
      // ... your other types
    ],
    // ... your other options
  }
}

And this is what your types array should look like if you use jasmine.

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{
  "compilerOptions": {
    "types": [
      "jasmine",
      // ... your other types
    ],
    // ... your other options
  }
}

If you still get the error after adding the typings with jasmine, try adding an import at the beginning of your test file:

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import 'jasmine';

And this is what your types array should look like if you use mocha.

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{
  "compilerOptions": {
    "types": [
      "mocha",
      // ... your other types
    ],
    // ... your other options
  }
}

# Add your test files to the include array in tsconfig.json

If the error persists, 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:

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{
  "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.

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{
  "compilerOptions": {},
  "include": [
    "src/**/*",
    "tests/**/*"
  ],
}

You can also use glob patterns. Here is an example that includes files ending in .spec.ts and .test.ts.

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{
  "compilerOptions": {},
  "include": [
    "src/**/*",
    "**/*.spec.ts",
    "**/*.test.ts"
  ],
}

If you've also set the exclude array in your tsconfig.json file, make sure you haven't excluded your test files from being type checked.

For example, the following tsconfig.json file excludes files ending in .test.ts, and prevents you from using the describe() function in them.

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{
  "compilerOptions": {},
  "include": [
    "src/**/*"
  ],
  "exclude": [
    "**/*.test.ts"
  ],
}

You can resolve the issue by moving the pattern into your include array.

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{
  "compilerOptions": {},
  "include": [
    "src/**/*",
    "**/*.test.ts"
  ],
}

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.

# Import the test module into your test file

If the error persists, try to import the test module at the top of the files in which you use the describe() function.

For example, if you use jest, add the following line at the top of the file.

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import 'jest';

describe('example', () => {
  it('multiplies two numbers', () => {
    expect(5 * 5).toBe(25);
  });
});

If you use mocha, add the following import statement at the top of the file.

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import 'mocha';

describe('example', () => {
  it('multiplies two numbers', () => {
    expect(5 * 5).toBe(25);
  });
});

If the error persists, restart your IDE and development server.

# Install the typings for Node.js

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.

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npm i -D @types/node

Make sure the types array in your tsconfig.json file contains "node".

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{
  "compilerOptions": {
    "types": [
      // ... your other types
      "node"
    ],
  },
}

# Delete your node_modules and reinstall your dependencies

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.

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# 👇️  (Windows) delete node_modules and package-lock.json
rd /s /q "node_modules"
del package-lock.json
del -f yarn.lock

# 👇️  (macOS/Linux) delete node_modules and package-lock.json
rm -rf node_modules
rm -f package-lock.json
rm -f yarn.lock

# 👇️ clean npm cache
npm cache clean --force

npm install

Restart your IDE and development server if the error persists.