---
title: "Documentation Tests"
description: "Learn how to write and run documentation tests in Deno. This guide covers how to create testable code examples in documentation comments, type-checking documentation, and running doc tests with the Deno test runner."
oldUrl: /runtime/manual/testing/documentation/
---

Deno supports both type-checking evaluating your documentation examples.

This makes sure that examples within your documentation are up to date and
working.

The basic idea is this:

````ts
/**
 * # Examples
 *
 * ```ts
 * const x = 42;
 * ```
 */
````

The triple backticks mark the start and end of code blocks, the language is
determined by the language identifier attribute which may be any of the
following:

- `js`
- `javascript`
- `mjs`
- `cjs`
- `jsx`
- `ts`
- `typescript`
- `mts`
- `cts`
- `tsx`

If no language identifier is specified then the language is inferred from media
type of the source document that the code block is extracted from.

Another attribute supported is `ignore`, which tells the test runner to skip
type-checking the code block.

````ts
/**
 * # Does not pass type check
 *
 * ```typescript ignore
 * const x: string = 42;
 * ```
 */
````

If this example was in a file named foo.ts, running `deno test --doc foo.ts`
will extract this example, and then both type-check and evaluate it as a
standalone module living in the same directory as the module being documented.

To document your exports, import the module using a relative path specifier:

````ts
/**
 * # Examples
 *
 * ```ts
 * import { foo } from "./foo.ts";
 * ```
 */
export function foo(): string {
  return "foo";
}
````

For more guides on testing in Deno, check out:

- [Basic testing tutorial](/examples/testing_tutorial/)
- [Mocking data in tests tutorial](/examples/mocking_tutorial/)
- [Testing web applications tutorial](/examples/web_testing_tutorial/)