add test showing that TS caches files

cli/tests/compiler_api_test.ts

@@ -150,3 +150,25 @@ test("diagnosticsTest", async function () {
   assert(Array.isArray(diagnostics));
   assert(diagnostics.length === 1);
 });
+
+test(async function compileChangedFile() {
+  const source1 = "console.log(1);";
+  const source2 = "console.log(2);";
+  const tempDir = await Deno.makeTempDir();
+  const filename = tempDir + "/test.ts";
+  const jsFilename = "file://" + tempDir + "/test.js";
+  const encoder = new TextEncoder();
+
+  await Deno.writeFile(filename, encoder.encode(source1));
+  const [diagnostics1, emitMap1] = await compile(filename);
+  console.log(jsFilename, emitMap1);
+  assert(!diagnostics1);
+  assert(emitMap1[jsFilename]);
+
+  await Deno.writeFile(filename, encoder.encode(source2));
+  const [diagnostics2, emitMap2] = await compile(filename);
+  assert(!diagnostics2);
+  assert(emitMap2[jsFilename]);
+
+  assert(emitMap1[jsFilename] !== emitMap2[jsFilename]);
+});