test: ensure that JS files are part of bundle too

- ensures that TS understands the JS w/ DTS w/o error
- and that rpt2 filters out JS while Rollup still resolves it on its own (since Rollup understands ESM)
  - similar to testing w/ a different plugin (i.e. literally testing an "integration"), but this is native Rollup behavior in this case where it doesn't need a plugin to understand ESM
- also the first test of actual code contents

- reformat the cache test a bit into its own block since we now have ~3 different sets of tests in the suite

Author: agilgur5

__tests__/integration/fixtures/no-errors/index.ts

@@ -4,3 +4,5 @@ export function sum(a: number, b: number) {
 
 export { difference } from "./some-import"
 export type { num } from "./type-only-import"
+
+export { identity } from "./some-js-import"

__tests__/integration/fixtures/no-errors/some-js-import.d.ts

@@ -0,0 +1,4 @@
+// TS needs a declaration in order to understand the import
+// but this is ambient, and so should not be directly imported into rpt2, just found by TS
+
+export function identity(a: any): any;

__tests__/integration/fixtures/no-errors/some-js-import.js

@@ -0,0 +1,5 @@
+// should be filtered out by rpt2, but still bundled by Rollup itself (as this is ESM, no need for a plugin)
+
+export function identity(a) {
+  return a;
+}

__tests__/integration/index.spec.ts

@@ -44,12 +44,15 @@ async function genBundle (input: string, extraOpts?: RPT2Options) {
 
 test("integration - no errors", async () => {
   const { output } = await genBundle("fixtures/no-errors/index.ts", { clean: true });
+
   // populate the cache
   await genBundle("fixtures/no-errors/index.ts");
   const { output: outputWithCache } = await genBundle("fixtures/no-errors/index.ts");
-
   expect(output).toEqual(outputWithCache);
 
+  // JS file should be bundled by Rollup, even though rpt2 does not resolve it (as Rollup natively understands ESM)
+  expect(output[0].code).toEqual(expect.stringContaining("identity"));
+
   expect(output[0].fileName).toEqual("index.ts");
   expect(output[1].fileName).toEqual("index.d.ts");
   expect(output[2].fileName).toEqual("index.d.ts.map");
@@ -66,12 +69,12 @@ test("integration - no errors - no declaration maps", async () => {
     tsconfigOverride: noDeclarationMaps,
     clean: true,
   });
+
   // populate the cache
   await genBundle("fixtures/no-errors/index.ts", { tsconfigOverride: noDeclarationMaps });
   const { output: outputWithCache } = await genBundle("fixtures/no-errors/index.ts", {
     tsconfigOverride: noDeclarationMaps,
   });
-
   expect(output).toEqual(outputWithCache);
 
   expect(output[0].fileName).toEqual("index.ts");
@@ -88,12 +91,12 @@ test("integration - no errors - no declarations", async () => {
     tsconfigOverride: noDeclarations,
     clean: true,
   });
+
   // populate the cache
   await genBundle("fixtures/no-errors/index.ts", { tsconfigOverride: noDeclarations });
   const { output: outputWithCache } = await genBundle("fixtures/no-errors/index.ts", {
     tsconfigOverride: noDeclarations,
   });
-
   expect(output).toEqual(outputWithCache);
 
   expect(output[0].fileName).toEqual("index.ts");