fix(typescript): resolve relative imports from transpiled .ts test files

.gitignore

@@ -9,8 +9,8 @@ reports/
 # Mutation testing temp files
 .stryker-tmp
 
-# TypeScript transpilation cache
-.testy-cache
+# TypeScript transpilation temporary files
+*.ts.testy-tmp.js
 
 # JSDoc
 doc/jsdoc/

lib/typescript/typescript_transpiler.js

@@ -9,12 +9,8 @@ export class TypescriptTranspiler {
     const tsCode = fs.readFileSync(filePath, 'utf8');
     const jsCode = await this.transpileTypeScript(tsCode);
 
-    const tempDir = path.join(process.cwd(), '.testy-cache');
-    if (!fs.existsSync(tempDir)) {
-      fs.mkdirSync(tempDir, { recursive: true });
-    }
-
-    const tempFilePath = path.join(tempDir, `${path.basename(filePath)}.js`);
+    // Written next to the original so relative imports keep resolving against the same directory.
+    const tempFilePath = path.join(path.dirname(filePath), `${path.basename(filePath)}.testy-tmp.js`);
     fs.writeFileSync(tempFilePath, jsCode);
 
     return { importPath: tempFilePath };

tests/core/fixtures/loader_fixture_dependency.ts

@@ -0,0 +1,2 @@
+// Fixture used by test_file_loader_test.js: a local TypeScript module imported by another fixture.
+export const dependencyMarker: string = 'loader-fixture-dependency-ts';

tests/core/fixtures/loader_fixture_imports_local.ts

@@ -0,0 +1,4 @@
+// Fixture used by test_file_loader_test.js: a TypeScript module that imports a sibling module via a relative path.
+import { dependencyMarker } from './loader_fixture_dependency.ts';
+
+export const importedMarker: string = dependencyMarker;

tests/core/test_file_loader_test.js

@@ -78,6 +78,16 @@ suite('TestFileLoader', () => {
     });
   });
 
+  test('loads a TypeScript file that imports a sibling module through a relative path', async() => {
+    await withRunner(async runner => {
+      const loader = new TestFileLoader(ui, runner);
+
+      await loader.loadAll([fixturesDir], /loader_fixture_imports_local\.ts$/u);
+
+      assert.that(fakeProcess.lastExitCode()).isNull();
+    });
+  });
+
   test('uses the injected module loader to evaluate matched files', async() => {
     await withRunner(async runner => {
       const seen = [];