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# Command Registration
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The command registration capability provides the core Vue CLI plugin functionality that integrates Jest testing with the Vue CLI service infrastructure.
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## Capabilities
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### Main Plugin Function
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The primary entry point that registers the `test:unit` command with Vue CLI service.
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```javascript { .api }
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/**
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 * Main Vue CLI plugin function that registers test:unit command
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 * @param api - Vue CLI Plugin API for registering commands and services
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 */
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function plugin(api: PluginAPI): void;
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```
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**Usage Example:**
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```javascript
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// Main plugin entry point (index.js)
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module.exports = api => {
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  api.registerCommand('test:unit', {
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    description: 'run unit tests with jest',
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    usage: 'vue-cli-service test:unit [options] <regexForTestFiles>',
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    options: {
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      '--watch': 'run tests in watch mode'
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    },
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    details: 'All jest command line options are supported.'
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  }, (args, rawArgv) => {
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    // Set environment variables for Babel
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    process.env.VUE_CLI_BABEL_TARGET_NODE = true
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    process.env.VUE_CLI_BABEL_TRANSPILE_MODULES = true
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    require('jest').run(rawArgv)
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  })
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}
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```
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### Command Registration
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Registers a new command with the Vue CLI service.
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```javascript { .api }
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/**
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 * Register a command with Vue CLI service
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 * @param name - Command name (e.g., 'test:unit')
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 * @param options - Command configuration and metadata
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 * @param handler - Function to execute when command is run
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 */
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registerCommand(
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  name: string,
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  options: CommandOptions,
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  handler: CommandHandler
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): void;
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```
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### Default Modes Configuration
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Specifies the default mode for the test:unit command.
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```javascript { .api }
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/**
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 * Default modes configuration for plugin commands
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 */
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const defaultModes: Record<string, string>;
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```
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**Usage Example:**
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```javascript
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module.exports.defaultModes = {
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  'test:unit': 'test'
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}
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```
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## Types
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```javascript { .api }
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interface PluginAPI {
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  /** Register a new command with Vue CLI service */
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  registerCommand(
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    name: string,
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    options: CommandOptions,
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    handler: CommandHandler
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  ): void;
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}
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interface CommandOptions {
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  /** Human-readable description of the command */
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  description: string;
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  /** Usage syntax example */
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  usage: string;
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  /** Available command-line options */
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  options: Record<string, string>;
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  /** Detailed help information */
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  details: string;
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}
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/**
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 * Command handler function
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 * @param args - Parsed command arguments
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 * @param rawArgv - Raw command line arguments array
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 */
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type CommandHandler = (args: any, rawArgv: string[]) => void;
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```
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## Environment Variables
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The plugin automatically sets these environment variables when running tests:
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```javascript { .api }
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interface TestEnvironmentVariables {
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  /** Configure Babel to target Node.js environment */
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  VUE_CLI_BABEL_TARGET_NODE: "true";
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  /** Enable Babel module transpilation for tests */
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  VUE_CLI_BABEL_TRANSPILE_MODULES: "true";
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}
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```
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## Command Execution
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The `test:unit` command supports all Jest CLI options and passes them through directly:
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**Common Usage Patterns:**
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```bash
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# Basic test execution
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vue-cli-service test:unit
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# Watch mode for development
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vue-cli-service test:unit --watch
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# Generate coverage reports
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vue-cli-service test:unit --coverage
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# Run specific test patterns
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vue-cli-service test:unit --testNamePattern="MyComponent"
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# Update snapshots
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vue-cli-service test:unit --updateSnapshot
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# Run tests matching specific files
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vue-cli-service test:unit tests/unit/components/
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```