> For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt.

# Rstest core

Rstest offers these core methods.

## defineConfig

This function helps you to autocomplete configuration types. It accepts a Rstest config object, or a function that returns a config.

- **Type:**

```ts
function defineConfig(config: RstestConfig): RstestConfig;
function defineConfig(config: () => RstestConfig): () => RstestConfig;
function defineConfig(
  config: () => Promise<RstestConfig>,
): () => Promise<RstestConfig>;
```

- **Examples:**

Pass a config object directly:

```ts
import { defineConfig } from '@rstest/core';

export default defineConfig({
  testTimeout: 10000,
  coverage: {
    enabled: true,
    provider: 'istanbul',
  },
});
```

Return a config from a synchronous factory:

```ts
import { defineConfig } from '@rstest/core';

export default defineConfig(() => ({
  testTimeout: 10000,
}));
```

Return a config from an asynchronous factory:

```ts
import { defineConfig } from '@rstest/core';

export default defineConfig(async () => ({
  testTimeout: 10000,
}));
```

## defineProject

This function helps you to autocomplete configuration types for [Rstest Project](/guide/basic/projects.md). It accepts a Rstest project config object, or a function that returns a config.

- **Type:**

```ts
type NestedProjectConfig = {
  projects: (InlineProjectConfig | string)[];
};

type ProjectConfigExport = ProjectConfig | NestedProjectConfig;

function defineProject(config: ProjectConfig): ProjectConfig;
function defineProject(config: NestedProjectConfig): NestedProjectConfig;
function defineProject(
  config: () => ProjectConfigExport,
): () => ProjectConfigExport;
function defineProject(
  config: () => Promise<ProjectConfigExport>,
): () => Promise<ProjectConfigExport>;
```

- **Examples:**

Pass a project config object directly:

```ts
import { defineProject } from '@rstest/core';

export default defineProject({
  root: './apps/web',
  testTimeout: 15000,
});
```

Return a project config from a synchronous factory:

```ts
import { defineProject } from '@rstest/core';

export default defineProject(() => ({
  root: './apps/web',
  testEnvironment: 'node',
}));
```

Return a project config from an asynchronous factory:

```ts
import { defineProject } from '@rstest/core';

export default defineProject(async () => ({
  root: './apps/web',
  testEnvironment: 'node',
}));
```

Define multiple nested projects:

```ts
import { defineProject } from '@rstest/core';

export default defineProject({
  projects: [
    {
      name: 'web',
      root: './apps/web',
    },
    {
      name: 'server',
      root: './apps/server',
    },
  ],
});
```

Use `defineProject` for the top-level export of a project config file. If that file returns a nested `projects` object, the object items inside `projects` are still inline projects.

Compared with `defineInlineProject`, `defineProject` does not require `name` on the top-level exported project. If `name` is omitted, Rstest will resolve it the same way as the [name](/config/test/name.md) option: first from the current project's `package.json`, then from the folder name.

## defineInlineProject


[Added in v0.9.6](https://github.com/web-infra-dev/rstest/releases/tag/v0.9.6)

This function helps you to autocomplete inline project configuration types inside `defineConfig({ projects: [...] })`. Inline projects must include a `name`.

Unlike `defineProject`, `defineInlineProject` is for object items inside a `projects` array. Inline projects must provide `name` explicitly because they do not have a standalone project root to infer it from.

- **Type:**

```ts
function defineInlineProject(config: InlineProjectConfig): InlineProjectConfig;
```

- **Example:**

```ts
import { defineConfig, defineInlineProject } from '@rstest/core';

export default defineConfig({
  projects: [
    defineInlineProject({
      name: 'web',
      root: './apps/web',
      testTimeout: 15000,
    }),
  ],
});
```

## mergeRstestConfig

Merge multiple Rstest config objects into a single config. It deeply merges each configuration object, automatically combining multiple function values into an array of sequentially executed functions, and returns a merged configuration object.

- **Type:**

```ts
function mergeRstestConfig(...configs: RstestConfig[]): RstestConfig;
```

- **Example:**

```ts
import { mergeRstestConfig } from '@rstest/core';

const config = mergeRstestConfig(
  {
    testTimeout: 5000,
  },
  {
    coverage: {
      enabled: true,
    },
  },
);
```

## mergeProjectConfig

Merge multiple Project config objects into a single config.

- **Type:**

```ts
function mergeProjectConfig(...configs: ProjectConfig[]): ProjectConfig;
```

- **Example:**

```ts
import { mergeProjectConfig } from '@rstest/core';

const config = mergeProjectConfig(
  {
    name: 'node',
    include: ['src/**/*.test.ts'],
  },
  {
    testTimeout: 10000,
  },
);
```

## loadConfig

Load Rstest configuration.

- **Type:**

```ts
function loadConfig(params?: {
  // Default is process.cwd()
  cwd?: string;
  // Specify the configuration file (relative or absolute path)
  path?: string;
  envMode?: string;
  configLoader?: 'auto' | 'jiti' | 'native';
}): Promise<{
  content: RstestConfig;
  filePath: string | null;
  dependencies: string[];
}>;
```

- **Example:**

```ts
import { loadConfig } from '@rstest/core';

const { content, filePath } = await loadConfig({
  cwd: './my-project',
  path: './rstest.config.ts',
});

console.log('Config loaded from:', filePath);
console.log('Config:', content);
```

If the Rstest config file does not exist in the cwd directory, the return value of the loadConfig method is `{ content: {}, filePath: null, dependencies: [] }`.