feat: enhance file format detection with error handling for unreadable files

Author: BrandonLWhite

src/__tests__/file-finder.test.ts

@@ -1,6 +1,6 @@
 import * as fs from 'fs';
 import * as path from 'path';
-import { findCoverageFiles } from '../file-finder';
+import { findCoverageFiles, FileFinder } from '../file-finder';
 
 // Mock @actions/glob
 jest.mock('@actions/glob', () => ({
@@ -246,5 +246,26 @@ describe('file-finder', () => {
       expect(files).toHaveLength(1);
       expect(files[0].format).toBe('json');
     });
+
+    it('should skip files that cannot be read for content detection', async () => {
+      // Create a file path that will trigger content detection but fail to read
+      const testPath = path.join(testDir, 'unreadable.xml');
+      // Write the file so statSync works (file exists check)
+      fs.writeFileSync(testPath, 'dummy content');
+
+      mockGlob.create.mockResolvedValue(createMockGlobber([testPath]));
+
+      const spySampleFileContent = jest.spyOn(FileFinder, 'sampleFileContent').mockImplementation(_ => {
+        throw new Error('EACCES: permission denied');
+      });
+
+      try {
+        const files = await findCoverageFiles('**/*.xml');
+        // The file should be skipped due to read error (returns null from detectCoverageFormat)
+        expect(files.some((f) => f.path === testPath)).toBe(false);
+      } finally {
+        spySampleFileContent.mockRestore();
+      }
+    });
   });
 });

src/file-finder.ts

@@ -7,7 +7,15 @@ export interface CoverageFile {
   format: string;
 }
 
-// Coverage format detection based on file patterns and content
+export class FileFinder {
+  /**
+   * Reads file content for format detection. Extracted for testability.
+   */
+  static sampleFileContent(filePath: string): string {
+    return fs.readFileSync(filePath, 'utf-8').slice(0, 2000); // Read first 2KB for detection
+  }
+}
+
 const FORMAT_PATTERNS: { pattern: RegExp; format: string; contentCheck?: (content: string) => boolean }[] = [
   // JaCoCo - XML format with jacoco in root element
   {
@@ -74,7 +82,7 @@ function detectFormat(filePath: string, content?: string): string | null {
   // Second pass: need to check content for files that require content checking
   if (!content && (filePath.endsWith('.xml') || filePath.endsWith('.json') || filePath.endsWith('.out'))) {
     try {
-      content = fs.readFileSync(filePath, 'utf-8').slice(0, 2000); // Read first 2KB for detection
+      content = FileFinder.sampleFileContent(filePath);
     } catch {
       return null;
     }