Do not throw error in launch.json does not exist (#4536)

For #332

Author: DonJayamanne

src/client/unittests/common/debugLauncher.ts

@@ -93,6 +93,9 @@ export class DebugLauncher implements ITestDebugLauncher {
         const workspaceFolder = this.workspaceService.workspaceFolders![0];
         const filename = path.join(workspaceFolder.uri.fsPath, '.vscode', 'launch.json');
         let configs: DebugConfiguration[] = [];
+        if (!(await this.fs.fileExists(filename))) {
+            return [];
+        }
         try {
             let text = await this.fs.readFile(filename);
             text = stripJsonComments(text);
@@ -105,7 +108,7 @@ export class DebugLauncher implements ITestDebugLauncher {
         } catch (exc) {
             traceError('could not get debug config', exc);
             const appShell = this.serviceContainer.get<IApplicationShell>(IApplicationShell);
-            await appShell.showErrorMessage('could not load unit test config from launch.json');
+            await appShell.showErrorMessage('Could not load unit test config from launch.json');
         }
         return configs;
     }

src/test/unittests/common/debugLauncher.unit.test.ts

@@ -175,9 +175,11 @@ suite('Unit Tests - Debug Launcher', () => {
             .returns(() => workspaceFolders[0]);
 
         if (!debugConfigs) {
-            filesystem.setup(fs => fs.readFile(TypeMoq.It.isAny()))
-                .throws(new Error('file not found'));
+            filesystem.setup(fs => fs.fileExists(TypeMoq.It.isAny()))
+                .returns(() => Promise.resolve(false));
         } else {
+            filesystem.setup(fs => fs.fileExists(TypeMoq.It.isAny()))
+                .returns(() => Promise.resolve(true));
             if (typeof debugConfigs !== 'string') {
                 debugConfigs = JSON.stringify({
                     version: '0.1.0',