moving our simple-git usage to a helper

.github/shared/src/simple-git.js

@@ -0,0 +1,13 @@
+import { simpleGit } from "simple-git";
+import { resolve } from "path";
+
+/**
+ *
+ * @param {string} inputPath
+ * @returns {Promise<string>}
+ */
+export async function getRootFolder(inputPath) {
+    // expecting users to handle the case where inputPath is not a git repo
+    const gitRoot = await simpleGit(inputPath).revparse("--show-toplevel");
+    return resolve(gitRoot.trim());
+}

.github/shared/test/simple-git.test.js

@@ -0,0 +1,24 @@
+import path from 'path';
+import os from 'os';
+import { mkdtemp, rm } from 'fs/promises';
+import { getRootFolder } from '../src/simple-git.js';
+import { describe, expect, it } from "vitest";
+
+describe('getRootFolder', () => {
+  it('resolves to repo root from a nested folder', async () => {
+    // Use __dirname (this test file directory) as input to getRootFolder
+    const testDir = __dirname;
+    const calculatedRoot = await getRootFolder(testDir);
+    // Expect the repository root 3 levels up from this test file
+    const expectedRoot = path.resolve(path.join(__dirname, '..', '..', '..'));
+    expect(calculatedRoot).toBe(expectedRoot);
+  });
+
+  it('throws when directory is not a git repository', async () => {
+    // Use async mkdtemp from fs/promises
+    const tempDir = await mkdtemp(path.join(os.tmpdir(), 'non-git-'));
+    await expect(getRootFolder(tempDir)).rejects.toThrow();
+    // Cleanup the temp directory
+    await rm(tempDir, { recursive: true, force: true });
+  });
+});