How to mock a function to test persist into database by PHPunit in Symfony

To answer your question:

Mocked methods are not the methods you want to test but the methods you do not want to test. In your code, you are creating a mock object of the class you want to test (which is totally fine though you usually mock dependent classes you do not want to test) and tell the mock object, that newUser() is a method you want to mock.

Instead, you want to test newUser() and probably want to test persistEntity():

$account_bm =$this->getMockBuilder('AccountBM')
            ->setMethods(array('persistEntity'))
            ->disableOriginalConstructor()
            ->getMock();
$account=$account_bm->newUser($account);

You might also want to go through PHPUnits Documentation about mock objects: https://phpunit.de/manual/current/en/test-doubles.html

Second, a few tips for developing with PHPUnit:

In your test you have quite a lot of assertions. The best case scenario ist to have only one assertion per test and PHPUnit actually helps you with that quite nicely, because it is able to compare pretty much everything. So instead of asserting every single value of you object, you can just assert one object with the other and PHPUnit will show you the differences if those objects are not equal.

Plus, you might even want to leave out some information in your entity you do not need. Your database might need a first and a last name, but your method doesn't so your test also doesn't. You won't have to write that much code and it's more readable.

But that's not all, assertions can also be done with mocked methods.

Try your test like this:

public function testNewUser() {
    // this is the entity for the method
    $account = new Account();
    $account->setEmail ( "[email protected]" );
    $account->setPassword ( "test" );

    // this is how the entity should look like when it's done
    $expectedAccount = new Account ();
    $expectedAccount ->setEmail ( "[email protected]" );
    $expectedAccount ->setInviationCode ( md5("[email protected]") );
    // changes needed, how does your encoder create the password hash?
    // Or even better: Also mock your encoder, you don't want to test it here
    $expectedAccount ->setPassword ( "test" );
    // As this is a random value, you might want to mock it as well
    // mock a static call
    $expectedAccount ->setSalt ( "10" );

    /** @var AccountBM|\PHPUnit_Framework_MockObject_MockObject $account_bm */
    $account_bm = $this->getMockBuilder('AccountBM')
        ->setMethods(array('persistEntity'))
        ->disableOriginalConstructor()
        ->getMockForAbstractClass();

    $account_bm->expects($this->once())
        ->method("persistEntity")
        ->with($expectedAccount);

    $account_bm->newUser($account);
}

You could now assert the returned entity with $expectedEntity, but I left that out to show you, that expecting a method to be called with specific parameters will already trigger an assertion.

As you will see, the above test will fail and show you which properties are wrong. Why is this the case?

Well there are two ToDos marked: Two of your values are generated by methods outside of your class, which should be mocked. Those are $this->encoder->encodePassword() and StringHelper::generateRandomString().

So create a mock object for the encoder and to mock a static method you put it in a separate method in AccountBM to wrap it:

AccountBm

public function newUser(Account $account) {
    $salt = $this->generateSalt("10");
    $account->setUsername ( $account->getEmail () );
    $invitation_code = hash ( 'md5', $account->getEmail () );
    $account->setInviationCode ( $invitation_code );
    $account->setPassword ( $this->encoder->encodePassword ( $account->getPassword (), $salt ) );
    $account->setSalt ( $salt );
    $this->persistEntity ( $account );
    return $account;
}

public function generateSalt($string)
{
    return StringHelper::generateRandomString ( $string );
}

And now mock this method together with the encoder:

public function testNewUser() {
    $account = new Account();
    $account->setEmail ( "[email protected]" );
    $account->setPassword ( "test" );

    $expectedAccount = new Account ();
    $expectedAccount ->setEmail ( "[email protected]" );
    $expectedAccount ->setInviationCode ( md5("[email protected]") );
    $expectedAccount ->setPassword ( "test" );
    $expectedAccount ->setSalt ( "10" );

    /** @var AccountBM|\PHPUnit_Framework_MockObject_MockObject $account_bm */
    $account_bm = $this->getMockBuilder('AccountBM')
        ->setMethods(array('persistEntity', 'generateSalt'))
        ->disableOriginalConstructor()
        ->getMockForAbstractClass();

    // mock the wrapper for the static method
    $account_bm->expects($this->once())
        ->method("generateSalt")
        ->with("10")
        ->will($this->returnValue("10"));

    // mock the encoder and set it to your object
    $encoder = $this->getMockBuilder("stdClass")
        ->setMethods(array("encodePassword"))
        ->disableOriginalConstructor()
        ->getMock();
    $encoder->expects($this->once())
        ->method("encodePassword")
        ->with("test", "10")
        ->will($this->returnValue(md5("test10")));
    $account_bm->setEncoder($encoder);

    $account_bm->expects($this->once())
        ->method("persistEntity")
        ->with($expectedAccount);

    $account_bm->newUser($account);
}

But the test is still failing - I'll leave it to you to replace the wrong values to check if you have understood how the code works ;-)