Allow mocked updates

Author: fhammerl

src/Runner.Listener/SelfUpdater.cs

@@ -182,14 +182,36 @@ private async Task DownloadLatestRunner(CancellationToken token)
 
             try
             {
-                archiveFile = await DownLoadRunner(latestRunnerDirectory, packageDownloadUrl, packageHashValue, token);
-
-                if (string.IsNullOrEmpty(archiveFile))
+#if DEBUG
+                // Much of the update process (targetVersion, archive) is server-side, this is a way to control it from here for testing specific update scenarios
+                // Add files like 'runner_v2.281.2.tar.gz' or 'runner_v2.283.0.zip' depending on your platform in your runner root folder
+                var isMockUpdate = StringUtil.ConvertToBoolean(Environment.GetEnvironmentVariable("GITHUB_ACTIONS_RUNNER_IS_MOCK_UPDATE"));
+                if (isMockUpdate)
                 {
-                    throw new TaskCanceledException($"Runner package '{packageDownloadUrl}' failed after {Constants.RunnerDownloadRetryMaxAttempts} download attempts");
+                    // the env var should be of format 'v2.281.2,v2.283.0,v2.283.1,v2.284.0'
+                    var mockVersions = Environment.GetEnvironmentVariable("GITHUB_ACTIONS_RUNNER_MOCK_VERSION_LIST").Split(',');
+                    if (mockVersions.Any()) 
+                    {
+                        var targetVersion = mockVersions.First();
+                        archiveFile = "runner_" + targetVersion;
+                        var newMockVersions = string.Join(",", mockVersions.Skip(1));
+                        Environment.SetEnvironmentVariable("GITHUB_ACTIONS_RUNNER_MOCK_VERSION_LIST", newMockVersions);
+                        _updateTrace.Add($"Mocking update with file: {archiveFile}, nothing is downloaded");
+                    }
                 }
+#else
+                // archiveFile is not null only if we mocked it above
+                if (archiveFile == null)
+                {
+                    archiveFile = await DownLoadRunner(latestRunnerDirectory, packageDownloadUrl, packageHashValue, token);
 
-                await ValidateRunnerHash(archiveFile, packageHashValue);
+                    if (string.IsNullOrEmpty(archiveFile))
+                    {
+                        throw new TaskCanceledException($"Runner package '{packageDownloadUrl}' failed after {Constants.RunnerDownloadRetryMaxAttempts} download attempts");
+                    }
+                    await ValidateRunnerHash(archiveFile, packageHashValue);
+                }
+#endif
 
                 await ExtractRunnerPackage(archiveFile, latestRunnerDirectory, token);
             }