Add and fix notebook extension unit tests (#10156)

extensions/notebook/src/test/common/stubs.ts

@@ -28,23 +28,23 @@ export class MockOutputChannel implements vscode.OutputChannel {
 	name: string;
 
 	append(value: string): void {
-		throw new Error('Method not implemented.');
+
 	}
 	appendLine(value: string): void {
-		throw new Error('Method not implemented.');
+
 	}
 	clear(): void {
-		throw new Error('Method not implemented.');
+
 	}
 	show(preserveFocus?: boolean): void;
 	show(column?: vscode.ViewColumn, preserveFocus?: boolean): void;
 	show(column?: any, preserveFocus?: any): void {
-		throw new Error('Method not implemented.');
+
 	}
 	hide(): void {
-		throw new Error('Method not implemented.');
+
 	}
 	dispose(): void {
-		throw new Error('Method not implemented.');
+
 	}
 }