Jest to JUnit XML Reporter

This challenge requires you to create a Jest reporter that transforms Jest's test results into the JUnit XML format. This is a common requirement for CI/CD pipelines and reporting tools that integrate with test execution frameworks, allowing for standardized reporting of test outcomes.

Problem Description

You need to develop a custom Jest reporter that intercepts Jest's test results and generates a JUnit XML report. The report should accurately reflect the success, failure, and skipped status of each test case.

Key Requirements:

• XML Structure: The output must conform to the JUnit XML schema. The root element should be <testsuites>, containing one or more <testsuite> elements. Each <testsuite> should contain multiple <testcase> elements.
• Test Suite Information: Each <testsuite> should include attributes for name (the test file name), tests (total number of tests in the suite), failures (number of failed tests), errors (number of tests with errors), skipped (number of skipped tests), and time (total execution time in seconds).
• Test Case Information: Each <testcase> should include attributes for name (the test name), classname (a descriptive identifier, often including the file path), and time (execution time in seconds).
• Failure Reporting: For failed tests, a <failure> element should be present within the <testcase>. This element should contain the failure message and potentially a stack trace (though the stack trace is optional for this challenge's core requirement).
• Error Reporting: For tests that result in errors (e.g., exceptions thrown outside of assertions), an <error> element should be present within the <testcase>, similar to <failure>.
• Skipped Tests: Skipped tests should be represented by a <skipped> element within the <testcase>.
• Integration with Jest: The reporter should be configurable within a Jest project.

Expected Behavior:

When Jest runs with your custom reporter enabled, it should output a valid JUnit XML file to a specified location or stdout.

Edge Cases to Consider:

• Tests that throw uncaught exceptions.
• Tests that are explicitly skipped.
• Test suites with no tests.
• Test files with no assertions (though Jest typically handles this).

Examples

Example 1: Simple Passing Test Suite

Input (Conceptual Jest Output):

{
  "numTotalTestSuites": 1,
  "numPassedTests": 2,
  "numFailedTests": 0,
  "numPendingTests": 0,
  "testResults": [
    {
      "testFilePath": "/path/to/my.test.ts",
      "testResults": [
        {
          "title": "should add two numbers",
          "status": "passed",
          "duration": 5,
          "ancestorTitles": ["MathUtils"]
        },
        {
          "title": "should subtract two numbers",
          "status": "passed",
          "duration": 3,
          "ancestorTitles": ["MathUtils"]
        }
      ],
      "startTime": 1678886400000,
      "endTime": 1678886408000,
      " கொண்டது": 0
    }
  ]
}

Output (JUnit XML):

<?xml version="1.0" encoding="UTF-8"?>
<testsuites tests="2" failures="0" errors="0" skipped="0" time="8.000">
  <testsuite name="my.test.ts" tests="2" failures="0" errors="0" skipped="0" time="8.000">
    <testcase name="should add two numbers" classname="MathUtils" time="5.000"/>
    <testcase name="should subtract two numbers" classname="MathUtils" time="3.000"/>
  </testsuite>
</testsuites>

Explanation:

The reporter generates a <testsuites> root element. Inside, a <testsuite> named my.test.ts is created, summarizing the total tests and time. Each passing test becomes a <testcase> with its name, classname, and duration.

Example 2: Suite with Failures and Skipped Tests

Input (Conceptual Jest Output):

{
  "numTotalTestSuites": 1,
  "numPassedTests": 1,
  "numFailedTests": 1,
  "numPendingTests": 1,
  "testResults": [
    {
      "testFilePath": "/path/to/complex.test.ts",
      "testResults": [
        {
          "title": "should pass",
          "status": "passed",
          "duration": 10,
          "ancestorTitles": ["FeatureA"]
        },
        {
          "title": "should fail due to assertion",
          "status": "failed",
          "duration": 15,
          "ancestorTitles": ["FeatureA"],
          "failureMessages": ["Expected true to be false"],
          "failureDetails": ["AssertionError: Expected true to be false\n    at Object.<anonymous> (/path/to/complex.test.ts:10:12)"]
        },
        {
          "title": "should be skipped",
          "status": "pending",
          "duration": 0,
          "ancestorTitles": ["FeatureA"]
        }
      ],
      "startTime": 1678887000000,
      "endTime": 1678887025000,
      " கொண்டது": 0
    }
  ]
}

Output (JUnit XML):

<?xml version="1.0" encoding="UTF-8"?>
<testsuites tests="3" failures="1" errors="0" skipped="1" time="25.000">
  <testsuite name="complex.test.ts" tests="3" failures="1" errors="0" skipped="1" time="25.000">
    <testcase name="should pass" classname="FeatureA" time="10.000"/>
    <testcase name="should fail due to assertion" classname="FeatureA" time="15.000">
      <failure message="Expected true to be false" type="AssertionError">AssertionError: Expected true to be false
    at Object.<anonymous> (/path/to/complex.test.ts:10:12)</failure>
    </testcase>
    <testcase name="should be skipped" classname="FeatureA" time="0.000">
      <skipped/>
    </testcase>
  </testsuite>
</testsuites>

Explanation:

The failed test includes a <failure> element with the message and stack trace. The skipped test has a <skipped/> element. The testsuites and testsuite elements are updated with the correct counts and total time.

Constraints

• The reporter must be implemented in TypeScript.
• The reporter should handle standard Jest test outcomes: passed, failed, and pending (which maps to skipped).
• The reporter should output valid XML that can be parsed by standard JUnit XML parsers.
• The reporter should be designed to be pluggable into Jest's custom reporter mechanism.
• The classname attribute for <testcase> should be derived from ancestorTitles in Jest's output, joined by dots. If ancestorTitles is empty, the classname can be derived from the test file name.

Notes

• You will need to understand Jest's reporter API. Specifically, the Reporter interface and its methods like onRunComplete.
• The structure of Jest's test results object will be crucial. You may want to familiarize yourself with the TestResult and AssertionResult interfaces provided by Jest.
• Consider using a small XML utility library for cleaner XML generation if you wish, or build the XML string manually.
• The type attribute for <failure> or <error> can be set to the type of error thrown (e.g., AssertionError). For simplicity, if no specific type is readily available, you can use a generic string like "Error".
• The time attribute should be in seconds, and it's a floating-point number. Ensure accurate conversion from milliseconds if Jest provides it.
• The JUnit XML specification allows for errors and failures. For this challenge, treat all uncaught exceptions that cause a test to fail as failures. If Jest distinguishes between these, you can adapt, but a unified approach to failures is acceptable.