Use 4 spaces for indentation in test applications

hello/hello.cpp

@@ -2,17 +2,17 @@
 
 class Hello {
 public:
-	Hello() {
-		printf("Hello ctor\n");
-	}
-	~Hello() {
-		printf("Hello dtor\n");
-	}
+    Hello() {
+        printf("Hello ctor\n");
+    }
+    ~Hello() {
+        printf("Hello dtor\n");
+    }
 };
 
 Hello global_h;
 
 int main(int argc, char* argv[]) {
-	std::cout<<"Hello world C++"<<std::endl;
-	return 0;
+    std::cout<<"Hello world C++"<<std::endl;
+    return 0;
 }