Add tests

test/fixtures/main-runner-order/app.js

@@ -0,0 +1,2 @@
+console.log("./app.js")
+module.exports = "./app.js"

test/fixtures/main-runner-order/app/index.js

@@ -0,0 +1,2 @@
+console.log("./app/index.js")
+module.exports = "./app/index.js"

test/fixtures/main-runner-order/app/test.js

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+'use strict';
+
+require('../../../common');
+const assert = require('assert');
+const child_process = require('child_process');
+
+async function spawnNodeRunner(path) {
+    return new Promise((resolve, reject) => {
+        child_process.exec(`node ${path}`, (err, stdout, stderr) => {
+            if (err) {
+                reject(err);
+            } else {
+                resolve(stdout);
+            }
+        });
+    });
+};
+
+async function main() {
+    assert.strictEqual((await spawnNodeRunner('.')).trim(), require('.').trim());
+}
+
+main();