Why std::async call behave like sync call with launch async policy? [duplicate]

This question already has an answer here:

• std::async doesn't work asynchronously 2 answers

Why async call behavelike sync call ?.In the below example mTest function called with std::sync with launch policy async & with normal thread one by one seperately.Why Both API behaviours are different in output?

#include <iostream>
#include <Test.h>
#include <future>

Test::Test()
{

}

Test::~Test()
{
}

void Test::doTest(){
    cout << std::this_thread::get_id() << " doTest" << endl;
//  std::async(std::launch::async, &Test::mTest, this);
    mThread = std::thread(&Test::mTest,this);
    cout << std::this_thread::get_id() << " after async call" << endl;
    if (mThread.joinable()) mThread.join();
}

bool Test::mTest()
{
    cout <<std::this_thread::get_id()<< " Asyn mTest called"<<endl;
    std::this_thread::sleep_for(chrono::milliseconds(10000));
    return true;
}

int main(int argc, char **argv) {
    Test test;
    test.doTest();
}

Output:

using async call

rajesh@rajesh:~/cpp_test$ ./test 
140079678486336 doTest
140079660783360 Asyn mTest called
140079678486336 after async call

using Thread call

rajesh@rajesh:~/cpp_test$ ./test 
139787779311424 doTest
139787779311424 after async call
139787761608448 Asyn mTest called