Testing - How this common scenario is classified and handled - php

Question

I’m just diving into testing/test driven development in php, and am a bit confused about how to handle a very typical scenario in our legacy codebase. Our codebase does not have many classes, it’s very functional programming oriented.
In this example code, which is pseudocode, I want to write a test for getAndOrderUsersByAge(). As you can see it first gets all the users from our database (in a giant array lets say, because we don’t have objects/classes) then sorts them. This is of course a VERY common occurrence in our code, manipulating or analyzing data gotten from the database; not objects, but an array of database rows basically.
Note that I've added an error in the if statement to simulate an error I want my tests to catch.
//gets all users in our db into an array, then sorts them by age
function getAndOrderUsersByAge(){
//get all users from the db
$all_users = getAllUsers();
//sort
$all_users_sorted = sortUsers($all_users)
//notice I've made a mistake here on purpose, left the "d" off of "$all_users_sorted"
//so the function will always return false, a mistake...which I want tests to catch
if(!empty($all_users_sorte){
return $all_users_sorted;
}
else{
return false;
}
}
My questions are:
1.) Is testing the function getAndOrderUsersByAge() unit testing, integration testing, or …?
2.) In my (unit?) test(s) of getAndOrderUsersByAge(), I want to assume that getAllUsers (the function which gets things from the db) behaves correctly because I only want to test getAndOrderUsersByAge() right? I’m not really sure what “concept” this falls under when I’m reading the two books I have on testing. Is this where I would “mock”, e.g. create some fake data for getAllUsers() to return?
3.) What tests would you write for getAndOrderUsersByAge()? I think I would write one that ensures a non-empty array is returned when getAllUsers() returns a non-empty array, as this would catch the error I've created. I'm not sure what else though.
Any tips, recommended reading material, etc. is very welcomed.

Answer 1

1.) Is testing the function getAndOrderUsersByAge() unit testing, integration testing, or …?
Any test that you do at code level is unit testing, basically testing methods , classes, interfaces. Tests that validate a unit or block of code.
2.) In my (unit?) test(s) of getAndOrderUsersByAge(), I want to assume that getAllUsers (the function which gets things from the db)
You can test getAndOrderUsersByAge() by actual data or mock data. Mock data is preferred so you will have more control on the test and you can create more test cases for sortUsers function.
3.) What tests would you write for getAndOrderUsersByAge()?
The test should be of nature that would validate your sortUsers function. I am not sure how your data looks but some tests could be:
1) data set that will have valid data , which will pass the test
2) data set that has invalid data like special characters in name
3) data set that has junk in age field or floating numbers or out of range integers, basically test how your function behaves when age has different type of data
4) data set that has null values
5) data set with 1 element array
6) data set with repeated element array
7) data set with invalid types in array