Add tests for Path function

src/jsutils/__tests__/Path-test.ts

@@ -0,0 +1,24 @@
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import type { Path } from '../Path';
+import { addPath, pathToArray } from '../Path';
+
+describe('Path', () => {
+  it('can add a new key to an existing Path', () => {
+    const first: Path = { prev: undefined, key: 1, typename: 'First' };
+    const second = addPath(first, 'two', 'Second');
+    expect(second.prev).to.equal(first);
+    expect(second.key).to.equal('two');
+    expect(second.typename).to.equal('Second');
+  });
+
+  it('can convert a Path to an array of its keys', () => {
+    const root: Path = { prev: undefined, key: 0, typename: 'Root' };
+    const first: Path = { prev: root, key: 'one', typename: 'First' };
+    const second: Path = { prev: first, key: 2, typename: 'Second' };
+    expect(pathToArray(second))
+      .to.be.an('array')
+      .that.deep.equals([0, 'one', 2]);
+  });
+});