Creates an empty .expected file when running test output compare

If the expected file does not already exists. This helps with test
creation and allows users to create tests more quickly.

Author: aeisenberg

extensions/ql-vscode/CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Fix a bug where archived source folders for databases were not showing any contents.
 - Fix URI encoding for databases that were created with special characters in their paths.
+- When comparing the results of a failed QL test run and the `.expected` file does not exist, an empty `.expected` file is created and compared against the `.actual` file.
 
 ## 1.3.4 - 22 October 2020
 

extensions/ql-vscode/src/test-ui.ts

@@ -1,10 +1,20 @@
 import * as fs from 'fs-extra';
 import * as path from 'path';
 import { Uri, TextDocumentShowOptions, commands, window } from 'vscode';
+import {
+  TestHub,
+  TestController,
+  TestAdapter,
+  TestRunStartedEvent,
+  TestRunFinishedEvent,
+  TestEvent,
+  TestSuiteEvent
+} from 'vscode-test-adapter-api';
+
+import { showAndLogWarningMessage } from './helpers';
 import { TestTreeNode } from './test-tree-node';
 import { DisposableObject } from './vscode-utils/disposable-object';
 import { UIService } from './vscode-utils/ui-service';
-import { TestHub, TestController, TestAdapter, TestRunStartedEvent, TestRunFinishedEvent, TestEvent, TestSuiteEvent } from 'vscode-test-adapter-api';
 import { QLTestAdapter, getExpectedFile, getActualFile } from './test-adapter';
 import { logger } from './logging';
 
@@ -78,12 +88,17 @@ export class TestUIService extends UIService implements TestController {
         preserveFocus: true,
         preview: true
       };
+
+      if (!await fs.pathExists(expectedPath)) {
+        showAndLogWarningMessage(`'${path.basename(expectedPath)}' does not exist. Creating an empty file.`);
+        await fs.createFile(expectedPath);
+      }
+
       if (await fs.pathExists(actualPath)) {
         const actualUri = Uri.file(actualPath);
         await commands.executeCommand<void>('vscode.diff', expectedUri, actualUri,
           `Expected vs. Actual for ${path.basename(testId)}`, options);
-      }
-      else {
+      } else {
         await window.showTextDocument(expectedUri, options);
       }
     }