Is testing constructor too much?

Question

Firstly, I will say that I come from the Java world (this is important, really).

I have been coding PHP for a while, one of the problems that I have encountered is that due to the lack of compilation, sometimes errors that could be easily detected at compilation time (for example, wrong number of parameters for a given function), can silently pass.

That could be easily detected as code coverage increases by adding unit tests. The question is, does it make sense for example to tests constructors in order to check that the passed parameters are correct? I do not mean only the number of parameters, but also the content of such parameters (for example, if a parameter is null, certain objects should launch an exception in order to avoid creating a "dirty" object).

Question is, am I too contaminated by years of Java code? Because after all, increasing the code coverage to "discover" missued functions feels like a (really) primitive way of compiling.

Also, I would like to note that I already use a development environment (PHPStorm), we are also using tools like PHPCodeSniffer.

Any ideas/suggestions?

Scissel

Answer 1

This is a good question that can be answered on a number of levels:

1. Language characteristics
2. Test coverage
3. CASE tools

1. Language characteristics As you have pointed out the characteristics of the PHP language differ markedly from the more strongly-typed languages such as Java. This raises a serious issue where programmers coming from the more strongly-typed languages such as Java and C# may not be aware of the implications of PHP's behaviour (such as those you have described). This introduces the possibility of mistakes on the part of the programmer (for example, a programmer who may have been less careful using Java because they know the compiler will catch incorrect parameters may not apply the appropriate care when developing in PHP). Consequently, better programmer education/supervision is needed to address this issue (such as in-house company coding standards, pair programming, code review). It also (as you have pointed out) raises the question of whether test coverage should be increased to check for such mistakes as would have been caught by a compiler.

2. Test Coverage The argument for test coverage is very project-specific. In the real world, the level of test coverage is primarily dictated by the error tolerance of the customer (which is dictated by the consequences of an error occuring in your system). If you are developing software that is to run on a real-time control system, then obviously you will test more. In your question you identify PHP as the language of choice; this could apply equally to the ever-increasing number of web-enabled frontends for critical systems infrastructure. On the other side of the coin, if you are developing a simple website for a model railroad club and are just developing a newsletter app then your customer may not care about the possibility of a bug in the constructor.

3. CASE Tools Ultimately it would be desirable for a CASE tool to be available which can detect these errors, such as missing parameters. If there are no suitable tools out there, why not create one of your own. The creation of a CASE tool is not out of reach of most programmers, particularly if you can hook into an open-source parsing engine for your language. If you are open-source inclined this may be a good project to kick start, or perhaps your company could market such a solution.

Conclusion In your case whether or not to test the constructors basically comes down to the question: what will the consequences of a failure in my system be? If it makes financial sense to expend extra resources on testing your constructors in order to avoid such failures, then you should do so. Otherwise it may be possible to get by with lesser testing such as pair programming or code reviews.

Nearsighted

Answer 2

Do you want the constructor to throw an exception if invalid parameters set? Do you want it to behave that same way tomorrow and next week and next year? Then you write a test to verify that it does.

Tests verify that your code behaves as you want it to. Failing on invalid parameters is code behavior just as much as calculating sales tax or displaying a user's profile page.

Midyear

Answer 3

We test constructors, as well as the order of the parameters, the defaults when not provided, and then some actual settings. For instance:

class UTIL_CATEGORY_SCOPE extends UTIL_DEPARTMENT_SCOPE
{
    function __construct($CategoryNo = NULL, $CategoryName = NULL)
    {
        parent::__construct();              // Do Not Pass fields to ensure that the array is checked when all fields are defined.
        $this->DeclareClassFields_();

        $this->CategoryName = $CategoryName;
        $this->CategoryNo   = $CategoryNo;
    }

    private function DeclareClassFields_()
    {
        $this->Fields['CategoryNo']             = new UTIL_ICAP_FIELD_PAIR_FIRST('CCL', 6, ML('Category'), 8);
        $this->Fields['CategoryName']           = new UTIL_ICAP_FIELD_PAIR_SECOND('CCL', 32, ML('Name'), 15, array(), array(), NULL, UTIL_ICAP_FIELD::EDIT_DENY, UTIL_ICAP_FIELD::UPDATE_DENY, 'DES');
    }
}

We then create our tests to not only check the constructor and its order, but that class and inheritance has not changed.

public function testObjectCreation()
    {
        $CategoryInfo = new UTIL_CATEGORY_SCOPE();
        $this->assertInstanceOf('UTIL_CATEGORY_SCOPE', $CategoryInfo);
        $this->assertInstanceOf('UTIL_DEPARTMENT_SCOPE', $CategoryInfo);
        $this->assertInstanceOf('UTIL_DATA_STRUCTURE', $CategoryInfo);     // Inherited from UTIL_DEPARTMENT_SCOPE
    }

    public function testConstructFieldOrder()
    {
        $CategoryInfo = new UTIL_CATEGORY_SCOPE(1500, 'Category Name');
        $this->assertEquals(1500, $CategoryInfo->CategoryNo);
        $this->assertEquals('Category Name', $CategoryInfo->CategoryName);
    }

    public function testConstructDefaults()
    {
        $CategoryInfo = new UTIL_CATEGORY_SCOPE();
        $this->assertNull($CategoryInfo->CategoryNo);
        $this->assertNull($CategoryInfo->CategoryName);
    }

    public function testFieldsCreated()
    {
        $CategoryInfo = new UTIL_CATEGORY_SCOPE();
        $this->assertArrayHasKey('CategoryNo', $CategoryInfo->Fields);
        $this->assertArrayHasKey('CategoryName', $CategoryInfo->Fields);
        $this->assertArrayHasKey('DeptNo', $CategoryInfo->Fields);      // Inherited from Parent
        $this->assertArrayHasKey('DeptName', $CategoryInfo->Fields);    // Inherited from Parent
    }

Choriamb