tessl/npm-nx--jest

Nx plugin for Jest testing with executors, generators, and configuration utilities for monorepo testing workflows.

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Configuration Management

Name: tessl/npm-nx--jest
Author: tessl

Utilities for programmatically modifying Jest configuration files using AST-based manipulation. These functions provide safe, type-aware methods for updating Jest configurations without manual string manipulation.

Capabilities

Config Property Management

Add or remove properties from Jest configuration files with full TypeScript AST support.

/**
 * Add a property to the Jest configuration file
 * @param host - Nx virtual file system tree
 * @param path - Path to Jest configuration file
 * @param propertyName - Property name or nested path (e.g., 'transform' or ['setupFilesAfterEnv', 0])
 * @param value - Value to set for the property
 * @param options - Configuration options for value handling
 */
function addPropertyToJestConfig(
  host: Tree,
  path: string,
  propertyName: string | string[],
  value: unknown,
  options?: { valueAsString: boolean }
): void;

/**
 * Remove a property from the Jest configuration file
 * @param host - Nx virtual file system tree
 * @param path - Path to Jest configuration file
 * @param propertyName - Property name or nested path to remove
 */
function removePropertyFromJestConfig(
  host: Tree,
  path: string,
  propertyName: string | string[]
): void;

Usage Examples:

import { addPropertyToJestConfig, removePropertyFromJestConfig } from "@nx/jest";
import { Tree } from '@nx/devkit';

// Add a simple property
addPropertyToJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  "verbose",
  true
);

// Add nested configuration
addPropertyToJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  ["transform", "^.+\\.vue$"],
  "vue-jest"
);

// Add array element
addPropertyToJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  ["setupFilesAfterEnv", 0],
  "<rootDir>/src/test-setup.ts"
);

// Add raw code as string
addPropertyToJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  "testMatch",
  "['<rootDir>/src/**/*.spec.ts']",
  { valueAsString: true }
);

// Remove properties
removePropertyFromJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  "verbose"
);

// Remove nested property
removePropertyFromJestConfig(
  tree,
  "apps/my-app/jest.config.ts",
  ["moduleNameMapper", "^@/(.*)$"]
);

AST Configuration Parsing

Parse Jest configuration files as TypeScript AST objects for advanced manipulation.

/**
 * Parse Jest configuration file content into a TypeScript AST object
 * @param configString - Raw content of Jest configuration file
 * @returns TypeScript ObjectLiteralExpression AST node
 */
function jestConfigObjectAst(configString: string): ts.ObjectLiteralExpression;

/**
 * Get Jest configuration object from file content
 * @param host - Nx virtual file system tree
 * @param path - Path to Jest configuration file
 * @returns Parsed Jest configuration object
 */
function jestConfigObject(
  host: Tree,
  path: string
): Partial<Config.InitialOptions> & { [index: string]: any };

/**
 * Add import statement to Jest configuration file
 * @param host - Nx virtual file system tree
 * @param path - Path to Jest configuration file
 * @param importStatement - Import statement to add at the top of the file
 */
function addImportStatementToJestConfig(
  host: Tree,
  path: string,
  importStatement: string
): void;

Usage Examples:

import { jestConfigObjectAst, jestConfigObject, addImportStatementToJestConfig } from "@nx/jest";

// Parse configuration as AST
const configContent = tree.read("jest.config.ts", "utf-8");
const configAst = jestConfigObjectAst(configContent);

// Now you can manipulate the AST directly
console.log(configAst.properties.length); // Number of configuration properties

// Get configuration as JavaScript object
const configObject = jestConfigObject(tree, "jest.config.ts");
console.log(configObject.testEnvironment); // Access configuration values

// Add import statement to configuration file
addImportStatementToJestConfig(
  tree,
  "jest.config.ts",
  "import { customMatcher } from './test-utils';"
);

Advanced AST Manipulation

Low-level functions for direct AST manipulation of Jest configuration objects.

/**
 * Add or update a property in a TypeScript object literal AST
 * @param tree - Nx virtual file system tree
 * @param object - TypeScript ObjectLiteralExpression to modify
 * @param properties - Array of property names for nested access
 * @param value - Value to set (as string representation)
 * @param path - File path for error reporting
 */
function addOrUpdateProperty(
  tree: Tree,
  object: ts.ObjectLiteralExpression,
  properties: string[],
  value: unknown,
  path: string
): void;

/**
 * Remove a property from a TypeScript object literal AST
 * @param tree - Nx virtual file system tree
 * @param object - TypeScript ObjectLiteralExpression to modify
 * @param properties - Array of property names for nested access
 * @param path - File path for error reporting
 */
function removeProperty(
  tree: Tree,
  object: ts.ObjectLiteralExpression,
  properties: string[],
  path: string
): void;

Usage Examples:

import { addOrUpdateProperty, removeProperty, jestConfigObjectAst } from "@nx/jest";

const configContent = tree.read("jest.config.ts", "utf-8");
const configObject = jestConfigObjectAst(configContent);

// Add nested property
addOrUpdateProperty(
  tree,
  configObject,
  ["coverageThreshold", "global", "branches"],
  "80",
  "jest.config.ts"
);

// Remove nested property
removeProperty(
  tree,
  configObject,
  ["transform", "^.+\\.jsx?$"],
  "jest.config.ts"
);

Common Configuration Patterns

Adding Test Environment Configuration

// Set test environment
addPropertyToJestConfig(tree, configPath, "testEnvironment", "jsdom");

// Add test environment options
addPropertyToJestConfig(
  tree,
  configPath,
  "testEnvironmentOptions",
  {
    customExportConditions: ["node", "require"]
  }
);

Configuring Module Resolution

// Add module name mapper
addPropertyToJestConfig(
  tree,
  configPath,
  ["moduleNameMapper", "^@/(.*)$"],
  "<rootDir>/src/$1"
);

// Add module file extensions
addPropertyToJestConfig(
  tree,
  configPath,
  "moduleFileExtensions",
  ["ts", "tsx", "js", "jsx", "json"]
);

Setting Up Transformations

// Add TypeScript transformation
addPropertyToJestConfig(
  tree,
  configPath,
  ["transform", "^.+\\.ts$"],
  ["ts-jest", { tsconfig: "<rootDir>/tsconfig.spec.json" }]
);

// Add file transformation for assets
addPropertyToJestConfig(
  tree,
  configPath,
  ["transform", "\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2)$"],
  "jest-transform-stub"
);

Coverage Configuration

// Set coverage directory
addPropertyToJestConfig(
  tree,
  configPath,
  "coverageDirectory",
  "coverage"
);

// Configure coverage reporters
addPropertyToJestConfig(
  tree,
  configPath,
  "coverageReporters",
  ["html", "text", "lcov"]
);

// Set coverage thresholds
addPropertyToJestConfig(
  tree,
  configPath,
  "coverageThreshold",
  {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80
    }
  }
);

Error Handling

The configuration management functions include built-in error handling:

File Not Found: Throws error if Jest configuration file doesn't exist
Parse Errors: Logs warnings and manual update instructions for invalid syntax
AST Manipulation Errors: Provides detailed error messages for failed property operations

try {
  addPropertyToJestConfig(tree, "invalid/path.ts", "testMatch", ["**/*.spec.ts"]);
} catch (error) {
  console.error("Failed to update Jest config:", error.message);
  // Error: Cannot find 'invalid/path.ts' in your workspace.
}

Property Name Formats

Property names can be specified in multiple formats:

// Simple property name
addPropertyToJestConfig(tree, path, "verbose", true);

// Dot-separated nested properties  
addPropertyToJestConfig(tree, path, "coverageThreshold.global.branches", 80);

// Array of property names for complex nesting
addPropertyToJestConfig(tree, path, ["transform", "^.+\\.vue$"], "vue-jest");

// Array indices for array properties
addPropertyToJestConfig(tree, path, ["setupFilesAfterEnv", 0], "./setup.ts");

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