fix: reporter writes current measured values via temp files instead of baselines

Author: iamAbhi-916

packages/@react-native-windows/perf-testing/src/ci/PerfJsonReporter.ts

@@ -78,11 +78,11 @@ export class PerfJsonReporter {
     const suites: SuiteResult[] = [];
 
     for (const suite of results.testResults) {
-      // Load the snapshot file for this test suite (written by toMatchPerfSnapshot)
-      const {file: snapshotFilePath} = SnapshotManager.getSnapshotPath(
+      // Load the CURRENT measured values written by toMatchPerfSnapshot
+      // to a temp file (not the baselines — those are for comparison only)
+      const snapshots = SnapshotManager.loadCurrentRun(
         suite.testFilePath,
       );
-      const snapshots = SnapshotManager.load(snapshotFilePath);
 
       const passed = suite.testResults.filter(
         t => t.status === 'passed',
@@ -136,6 +136,11 @@ export class PerfJsonReporter {
     );
 
     console.log(`\n📊 Perf results written to: ${this.outputFile}`);
+
+    // Clean up temp files written by test workers
+    for (const suite of results.testResults) {
+      SnapshotManager.cleanCurrentRun(suite.testFilePath);
+    }
   }
 }
 

packages/@react-native-windows/perf-testing/src/matchers/snapshotManager.ts

@@ -72,4 +72,50 @@ export class SnapshotManager {
   static buildKey(testName: string): string {
     return `${testName} 1`;
   }
+
+  /**
+   * Path to the temp file where the current run's measured values are stored.
+   * Written by toMatchPerfSnapshot (worker), read by PerfJsonReporter (main).
+   */
+  static getCurrentRunPath(testFilePath: string): string {
+    const testDir = path.dirname(testFilePath);
+    const snapshotDir = path.join(testDir, '__perf_snapshots__');
+    return path.join(
+      snapshotDir,
+      `${path.basename(testFilePath)}.perf-current.json`,
+    );
+  }
+
+  /**
+   * Record a single test's measured values to the current-run temp file.
+   * Called from the test worker process by toMatchPerfSnapshot.
+   */
+  static recordCurrentRun(
+    testFilePath: string,
+    key: string,
+    entry: SnapshotEntry,
+  ): void {
+    const currentPath = this.getCurrentRunPath(testFilePath);
+    const existing = this.load(currentPath);
+    existing[key] = entry;
+    this.save(currentPath, existing);
+  }
+
+  /**
+   * Load the current run's measured values from the temp file.
+   * Called from the main process by PerfJsonReporter.
+   */
+  static loadCurrentRun(testFilePath: string): SnapshotFile {
+    return this.load(this.getCurrentRunPath(testFilePath));
+  }
+
+  /**
+   * Remove the current-run temp file (cleanup after reporting).
+   */
+  static cleanCurrentRun(testFilePath: string): void {
+    const p = this.getCurrentRunPath(testFilePath);
+    if (fs.existsSync(p)) {
+      fs.unlinkSync(p);
+    }
+  }
 }

packages/@react-native-windows/perf-testing/src/matchers/toMatchPerfSnapshot.ts

@@ -192,6 +192,13 @@ expect.extend({
       };
     }
 
+    // Record current measured values for the CI reporter
+    SnapshotManager.recordCurrentRun(testPath, snapshotKey, {
+      metrics: received,
+      threshold,
+      capturedAt: new Date().toISOString(),
+    });
+
     // COMPARE MODE
     const {errors, warnings} = compareAgainstBaseline(
       received,