isolatedModules does not imply every file is a module (#54218)

src/compiler/utilities.ts

@@ -1857,7 +1857,7 @@ function isCommonJSContainingModuleKind(kind: ModuleKind) {
 
 /** @internal */
 export function isEffectiveExternalModule(node: SourceFile, compilerOptions: CompilerOptions) {
-    return isExternalModule(node) || getIsolatedModules(compilerOptions) || (isCommonJSContainingModuleKind(getEmitModuleKind(compilerOptions)) && !!node.commonJsModuleIndicator);
+    return isExternalModule(node) || (isCommonJSContainingModuleKind(getEmitModuleKind(compilerOptions)) && !!node.commonJsModuleIndicator);
 }
 
 /**

src/testRunner/unittests/services/transpile.ts

@@ -130,7 +130,7 @@ var x = 0;`, {
         testVerbatimModuleSyntax: true
     });
 
-    transpilesCorrectly("Generates module output", `var x = 0;`, {
+    transpilesCorrectly("Generates module output", `var x = 0; export {};`, {
         options: { compilerOptions: { module: ts.ModuleKind.AMD } }
     });
 
@@ -139,7 +139,7 @@ var x = 0;`, {
         testVerbatimModuleSyntax: true
     });
 
-    transpilesCorrectly("Sets module name", "var x = 1;", {
+    transpilesCorrectly("Sets module name", "var x = 1; export {};", {
         options: { compilerOptions: { module: ts.ModuleKind.System, newLine: ts.NewLineKind.LineFeed }, moduleName: "NamedModule" }
     });
 

src/testRunner/unittests/transform.ts

@@ -304,6 +304,7 @@ describe("unittests:: TransformAPI", () => {
                 target: ts.ScriptTarget.ES5,
                 module: ts.ModuleKind.System,
                 newLine: ts.NewLineKind.CarriageReturnLineFeed,
+                moduleDetection: ts.ModuleDetectionKind.Force,
             }
         }).outputText;