Add test runner for import.meta fields

tests/.gitignore

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+/node_modules

tests/README.md

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+# `import.meta` Tests
+
+These tests provide structured documentation on the expected behavior of different
+`import.meta` properties and their availability across different runtimes and tools.
+
+The code is organized as follows:
+
+1. `fixtures/`: Each file is a test scenario.
+1. `runtimes/`: How to run the scenarios in different runtimes/environments.
+1. `features/`: Code to test for different `import.meta` fields, given loaded fixtures.
+
+To run the tests in bun:
+
+```sh
+bun test
+```
+
+To run them in node.js:
+
+```sh
+npm install
+# Then:
+node --test **/*.spec.js
+# or:
+npm test
+```
+
+To write a summary of the current status, run `npm run test:report` which will
+update [report.md](./report.md).

tests/features/main.spec.js

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+import { expect, it } from "#test";
+
+import { describeMetaField } from "../runtimes.js";
+
+describeMetaField("main", ({ fixtures: { reflect, indirect } }) => {
+  it("is true for entry point", () => {
+    expect(reflect.meta.main).toBe(true);
+  });
+
+  it("is false for non-entry point", () => {
+    expect(indirect.meta.main).toBe(false);
+  });
+});

tests/features/url.spec.js

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+import { expect, it } from "#test";
+
+import { describeMetaField } from "../runtimes.js";
+
+describeMetaField("url", ({ baseURL, fixtures: { reflect, url__char } }) => {
+  it("correct URL for reflect.js", () => {
+    expect(reflect.meta.url).toBe(new URL(reflect.filename, baseURL).href);
+  });
+
+  it("escapes URL characters", () => {
+    expect(url__char.meta.url).toMatch(/\/url%20char\.js$/);
+  });
+});

tests/fixtures/indirect.js

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+import { printImportMeta } from "./util/print.js";
+
+import meta from './indirect/reflect.js';
+
+printImportMeta(meta);

tests/fixtures/indirect/reflect.js

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+export default import.meta;

tests/fixtures/reflect.js

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+import { printImportMeta } from "./util/print.js";
+
+printImportMeta(import.meta);

tests/fixtures/url char.js

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+import { printImportMeta } from "./util/print.js";
+
+printImportMeta(import.meta);

tests/fixtures/util/print.js

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+export function printImportMeta(metaObj) {
+  // Not all runtimes set meta properties has plain own properties.
+  const plainObject = {};
+  for (const key in metaObj) {
+    plainObject[key] = metaObj[key];
+  }
+
+  console.log(
+    JSON.stringify({
+      meta: plainObject,
+      ownMeta: { ...metaObj },
+    })
+  );
+}