fix(js): resolve Jest testMatch/testRegex configuration conflict

[mohammedahmed18]

Problem

When optimizing JavaScript/TypeScript projects with bundler moduleResolution, Jest would fail immediately with a configuration validation error:

Validation Error: Configuration options testMatch and testRegex cannot be used together.

This blocked ALL optimizations for affected projects since no tests could run to establish a behavioral baseline.

Root Cause

Two-stage Jest config generation caused conflicting options:

1. _create_codeflash_jest_config() creates a base config that includes testRegex (line 321)
2. _create_runtime_jest_config() extends this base config using spread operator:

   module.exports = {
     ...baseConfig,  // This spreads all properties, including testRegex!
     testMatch: ['**/*.test.ts', ...],  // Then adds testMatch - CONFLICT!
   }

3. Jest's validation rejects configs with both testMatch and testRegex

Solution

Explicitly set testRegex: undefined in the runtime config to override the inherited value:

module.exports = {
  ...baseConfig,
  testMatch: ['**/*.test.ts', ...],
  testRegex: undefined,  // Clear inherited testRegex to avoid conflict
}

Jest's config merging allows explicit undefined to override inherited values.

Testing

Before fix:

❌ Jest failed with returncode=1.
   Validation Error: Configuration options testMatch and testRegex cannot be used together.

After fix:

✅ Jest runs without configuration errors
✅ Validation passes
✅ Can proceed to test execution

Tested on n8n packages/workflow which uses bundler moduleResolution in TypeScript.

Impact

Fixes JavaScript/TypeScript optimization for projects that:

• Use TypeScript with moduleResolution: "bundler" (increasingly common in modern TypeScript projects)
• Trigger Codeflash's ESM compatibility config generation
• Use Jest as the test framework

Without this fix, these projects cannot be optimized at all.

Files Changed

• codeflash/languages/javascript/test_runner.py - Added testRegex: undefined in _create_runtime_jest_config()

Related

This fix resolves the configuration conflict, but there may be additional test result parsing issues to investigate separately (XML format compatibility).

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[claude]

Claude finished @mohammedahmed18's task in 2m 10s —— View job

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PR Review Summary

Prek Checks

Prek passes (ruff check + format). Mypy errors in test_runner.py are pre-existing and unrelated to this change.

Code Review

Size: SMALL (1 line)

The fix is correct and well-targeted. When _create_runtime_jest_config() spreads baseConfig (which may contain testRegex from _create_codeflash_jest_config()), adding testRegex: undefined at test_runner.py:396 overrides the inherited key and prevents Jest from seeing both testMatch and testRegex set simultaneously.

One concern — missing test:

Per the project's testing guidelines, bug fixes must include a test. The existing tests for _create_runtime_jest_config (at tests/test_languages/test_javascript_test_runner.py:1061) check moduleDirectories behavior but none verify the testRegex: undefined override.

A test should be added that:

1. Creates a base Jest config containing testRegex
2. Calls _create_runtime_jest_config() with that base config
3. Asserts the generated content includes testRegex: undefined

Fix this →

Duplicate Detection

No duplicates detected. The else branch (no base_config_path, line ~400) correctly omits testRegex entirely since there's no base config to inherit from — so the fix only needs to be in the if base_config_path branch.

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Last updated: 2026-04-02