How do you unit test if statements in angular

I have a function that subscribes a response from the NGRX store then uses the variable provided to change a message.

How do I test that the message changes when the variable updates?

getData() {
this.service.getPreferences().subscribe(res => {
this.mypreference$ = res.mypreference;
});
if (this.mypreference$ == false) {
(this.mypreferenceType = 'noPreference');
} else {
(this.mypreferenceType = 'Preference');
}
}

getPreferences() { return this.store.select('user').map((state: User) => state); }

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