chore(wpt): throw better error when wpt path does not exist

Author: jazelly

lib/github/tree.js

@@ -35,7 +35,15 @@ export default class GitHubTree {
       branch,
       path
     });
-    return data.repository.ref.target.history.nodes[0].oid;
+
+    const targetHistoryNodes = data.repository.ref.target.history.nodes;
+    if (!targetHistoryNodes.length) {
+      // Sometimes this function is in a spinner, and we need to print the error
+      // after a new line.
+      console.log();
+      throw new Error(`Cannot find WPT for "${path}". Please check the WPT name.`);
+    }
+    return targetHistoryNodes[0].oid;
   }
 
   /**

test/unit/wpt_updater.test.js

@@ -0,0 +1,51 @@
+import { describe, it, before, after } from 'node:test';
+import assert from 'node:assert';
+import TestCLI from '../fixtures/test_cli.js';
+import sinon from 'sinon';
+
+import { WPTUpdater } from '../../lib/wpt/index.js';
+
+describe('WPTUpdater', function() {
+  const UNKNOWN_PATH = 'unknown path';
+  let request;
+  let wptUpdater;
+  let nodedir;
+  let cli;
+  let path;
+  const emptyData = {
+    repository:
+    {
+      ref: { target: { history: { nodes: [] } } }
+    }
+  };
+
+  before(() => {
+    cli = cli = new TestCLI();
+    request = {
+      gql: sinon.stub()
+    };
+    nodedir = '.';
+    request.gql.withArgs(
+      'LastCommit',
+      { path: UNKNOWN_PATH }
+    ).returns(Promise.resolve(emptyData));
+  });
+
+  after(() => {
+    cli.clearCalls();
+  });
+
+  it('throws meaningful error when WPT name not found', async() => {
+    path = UNKNOWN_PATH;
+    wptUpdater = new WPTUpdater(path, cli, request, nodedir);
+    let thrown = null;
+    try {
+      await wptUpdater.update();
+    } catch (err) {
+      thrown = err;
+    }
+
+    assert(thrown instanceof Error);
+    assert(thrown.message, `Cannot find WPT for "${path}". Please check the WPT name.`);
+  });
+});