doubts on writing test case for a function - c++

Question

I have a function changeUserPassword() in user.cpp and I wanted to do a cppUnit test on it.
user.cpp
int User::changeUserPassword()
{
std::vector<user>::iterator it;
std::ifstream readFile("info.txt");
while(readFile >> userName >> password)
{
userDetails.push_back(user(userName,password));
}
readFile.close();
std::cout << "Please enter a user name that the password will be reset \n";
std::cin >> name;
it = std::find(userDetails.begin(),userDetails.end(),user(name,name));
if (it !=userDetails.end())
{
std::cout << "Please enter a new password" << std::endl;
std::cin >> newPassword;
it->setPassword(newPassword);
std::ofstream out("tempFile.txt");
for (it =userDetails.begin(); it !=userDetails.end(); it++) {
std::cout << it->getUserName() << " " << it->getPassword() << "\n";
out << it->getUserName() << " " << it->getPassword() << std::endl;
}
out.close();
remove("info.txt");
rename("tempfile.txt","info.txt");
}
else
{
it++;
}
return 0;
}
testcase.h
#ifndef TESTCASE_H
#define TESTCASE_H
#include "user.h"
#include <cppunit/TestCase.h>
#include <cppunit/extensions/HelperMacros.h>
class csci222TestCase : public CPPUNIT_NS::TestFixture {
CPPUNIT_TEST_SUITE(testcase);
CPPUNIT_TEST (testChangePassword);
CPPUNIT_TEST_SUITE_END();
public:
protected:
void testChangePassword(void);
private:
user testChangeUserPassword;
};
#endif
testcase.cpp
void testcase::testChangePassword(void) {
std::cout << "\n";
CPPUNIT_ASSERT_EQUAL(testChangeUserPassword.changeUserPassword(),0);
}
The thing is, I feel that the way I wrote my test case for changeUserPassword() isn't testing for anything. It's more like running the method and once it finished, it will return 0. How should I or what should I do to improve on the test case?

Answer 1

This function is not a good candidate for unit testing. It has file and user input for starters. You probably really only want to test the line
it->setPassword(newPassword);
which is actually what 'sets' the password, presumably. For that you would call the function in the unit test with a given password, then in turn do a getPassword() and see if it was changed to what you expected.
If you really want to test that function as-is, you would need to look into stubs and/or mock objects. For that you would need to refactor your code with some simple dependency injection, so you could swap the disk file I/O with some memory file I/O, for example. But I don't recommend this path.
To address the more conceptual issue that you have, your testChangePassword() function should just check that the password was changed. As it stands, all you're really testing for, in effect, is that the function doesn't throw an exception.
To sum up, your unit test should ideally be of the form:
user testuser;
testuser.setPassword( "Fred");
std::string pwd = testuser.getPassword();
CPPUNIT_ASSERT_EQUAL( "Fred", pwd);

Answer 2

In your case you should also try:
1. changing a password several times.
2. changing password to the same password.
3. changing a non existing password.
4. Changing the password on one with illegal characters.
5. Reading from a non-existing file.
6. Reading an invalid format of data from the file.
7. Check that you clean all fields of the your object unnecessary data when you complete the function.