Add auto test debug mode for launch.json (#1780) (#1832)

* Add auto `test` debug mode for launch.json(#1780)

check filename to get debug mode

* Remove redundant `else` and add check for null activeEditor

src/goDebugConfiguration.ts

@@ -24,8 +24,8 @@ export class GoDebugConfigurationProvider implements vscode.DebugConfigurationPr
 	}
 
 	public resolveDebugConfiguration?(folder: vscode.WorkspaceFolder | undefined, debugConfiguration: vscode.DebugConfiguration, token?: vscode.CancellationToken): vscode.DebugConfiguration {
+		const activeEditor = vscode.window.activeTextEditor;
 		if (!debugConfiguration || !debugConfiguration.request) { // if 'request' is missing interpret this as a missing launch.json
-			let activeEditor = vscode.window.activeTextEditor;
 			if (!activeEditor || activeEditor.document.languageId !== 'go') {
 				return;
 			}
@@ -54,6 +54,10 @@ export class GoDebugConfigurationProvider implements vscode.DebugConfigurationPr
 			debugConfiguration['dlvLoadConfig'] = dlvConfig['dlvLoadConfig'];
 		}
 
+		if (activeEditor && activeEditor.document.fileName.endsWith('_test.go')) {
+			debugConfiguration['mode'] = 'test';
+		}
+
 		return debugConfiguration;
 	}