Revert "no cached readfile"

This reverts commit 00c572a.

packages/jest-runtime/src/index.ts

@@ -641,7 +641,7 @@ class Runtime {
     moduleRegistry: ModuleRegistry,
   ) {
     if (path.extname(modulePath) === '.json') {
-      const text = stripBOM(fs.readFileSync(modulePath, 'utf8'));
+      const text = stripBOM(this.readFile(modulePath));
 
       const transformedFile = this._scriptTransformer.transformJson(
         modulePath,
@@ -1059,14 +1059,16 @@ class Runtime {
     filename: string,
     options?: InternalModuleOptions,
   ): string {
+    const source = this.readFile(filename);
+
     if (options?.isInternalModule) {
-      return this._cacheFS[filename] ?? fs.readFileSync(filename, 'utf8');
+      return source;
     }
 
     const transformedFile = this._scriptTransformer.transform(
       filename,
       this._getFullTransformationOptions(options),
-      this._cacheFS[filename],
+      source,
     );
 
     this._fileTransforms.set(filename, transformedFile);
@@ -1636,6 +1638,18 @@ class Runtime {
       xtest: this._environment.global.xtest,
     };
   }
+
+  private readFile(filename: Config.Path): string {
+    let source = this._cacheFS[filename];
+
+    if (!source) {
+      source = fs.readFileSync(filename, 'utf8');
+
+      this._cacheFS[filename] = source;
+    }
+
+    return source;
+  }
 }
 
 function invariant(condition: unknown, message?: string): asserts condition {