Unit testing of a class reading a configuration file - unit-testing

Question

I have a class "Configuration" that has a method "getConfig" that reads a configuration file "config.ini" where I have all the app configs (database credentials and host, some apis keys, .....)
For now I have this unit test that tests if the database entry exists in the config file and at the same time confirms that the array returned by the method "getConfig" has the key "database":
function testConfigFileHasDatabaseEntry()
{
$configuration = Configuration::getInstance();
$arrConfig = $configuration->getConfig();
$this->assertArrayHasKey('database', $arrConfig);
}
I have also another unit test that confirms that "getConfig" returns a variable of type array.
My question is the following:
In terms of unit testing best practices, in this case is this test enough to confirm that the function getConfig is well tested or it is better to confirm that every key exists in the config file. I think confirming that all entries are in the config file maybe falls under another category of testing, but I want to be sure.
Let me know what is the best practice in this case.
Base on the answer of gcontrollez I realized it is better to post the class source code:
<?php
/**
* Loads the configuration file
*/
namespace Example\Lib;
class Configuration {
private static $instance;
private $arrConfig;
/**
* Constructor: loads the config file into property arrConfig and dies if unable
* to load config file
*
* #return void
*/
private function __construct()
{
$this->arrConfig = parse_ini_file("config/settings.ini", true);
if ($this->arrConfig == false){
die("Cannot load configuration file");
}
}
/**
* returns an instance of this singleton class
*
* #return Configuration
*/
public static function getInstance()
{
if (self::$instance == null){
self::$instance = new Configuration();
}
return self::$instance;
}
/**
* Getter for the property arrConfig
*
* #return array:
*/
public function getConfig() {
return $this->arrConfig;
}
}
Thanks

Answer 1

You are not unit testing the getConfig method. You are just checking that its result contains certain data. This is perfectly valid and can be useful but is not a unit test.
If you wanted to unit test the getConfig method, you should check it's behaviour with each possible config.ini file. I suppose you are using the parse_ini_file function inside getConfig. So in order to unit test the getConfig method you should check all the possible cases you think that can happen:
- testConfigFileIsLoaded
- testExceptionThrownIfConfigFileFailsToLoad
The parse_ini_file returns an array or false so those are the cases that you should check.
For that you need to be able to change the .ini file to be used. If it's harcoded inside the Configuration class you wont be able to do that.