test_runner: support module detection in module mocks

PR-URL: #53642
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: GeoffreyBooth

lib/internal/test_runner/mock/mock.js

@@ -513,7 +513,9 @@ class MockTracker {
 mockSpecifier,caller,null,
 );
 debug('module mock, url = "%s", format = "%s", caller = "%s"',url,format,caller);
-validateOneOf(format,'format',kSupportedFormats);
+if(format){// Format is not yet known for ambiguous files when detection is enabled.
+validateOneOf(format,'format',kSupportedFormats);
+}
 constbaseURL=URL.parse(url);
 
 if(!baseURL){

lib/test/mock_loader.js

@@ -143,26 +143,34 @@ async function load(url, context, nextLoad) {
 constbaseURL=parsedURL ? parsedURL.href : url;
 constmock=mocks.get(baseURL);
 
+constoriginal=awaitnextLoad(url,context);
 debug('load hook, mock = %o',mock);
 if(mock?.active!==true){
-returnnextLoad(url);
+returnoriginal;
 }
 
 // Treat builtins as commonjs because customization hooks do not allow a
 // core module to be replaced.
-constformat=mock.format==='builtin' ? 'commonjs' : mock.format;
+// Also collapse 'commonjs-sync' and 'require-commonjs' to 'commonjs'.
+constformat=(
+original.format==='builtin'||
+original.format==='commonjs-sync'||
+original.format==='require-commonjs') ? 'commonjs' : original.format;
 
-return{
+constresult={
 __proto__: null,
  format,
 shortCircuit: true,
-source: awaitcreateSourceFromMock(mock),
+source: awaitcreateSourceFromMock(mock,format),
 };
+
+debug('load hook finished, result = %o',result);
+returnresult;
 }
 
-asyncfunctioncreateSourceFromMock(mock){
+asyncfunctioncreateSourceFromMock(mock,format){
 // Create mock implementation from provided exports.
-const{ exportNames,format,hasDefaultExport, url }=mock;
+const{ exportNames, hasDefaultExport, url }=mock;
 constuseESM=format==='module';
 constsource=`${testImportSource(useESM)}
 if (!$__test.mock._mockExports.has('${url}')) {