The correct way to avoid SQL injection attacks, no matter which database you use, is to separate the data from SQL, so that data stays data and will never be interpreted as commands by the SQL parser. It is possible to create SQL statement with correctly formatted data parts, but if you don't fully understand the details, you should always use prepared statements and parameterized queries. These are SQL statements that are sent to and parsed by the database server separately from any parameters. This way it is impossible for an attacker to inject malicious SQL.

You basically have two options to achieve this:

1. Using PDO (for any supported database driver):

    $stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
   
    $stmt->execute([ 'name' => $name ]);
   
    foreach ($stmt as $row) {
        // Do something with $row
    }
   

2. Using MySQLi (for MySQL):

    $stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
    $stmt->bind_param('s', $name); // 's' specifies the variable type => 'string'
   
    $stmt->execute();
   
    $result = $stmt->get_result();
    while ($row = $result->fetch_assoc()) {
        // Do something with $row
    }
   

If you're connecting to a database other than MySQL, there is a driver-specific second option that you can refer to (for example, pg_prepare() and pg_execute() for PostgreSQL). PDO is the universal option.

Correctly setting up the connection

Note that when using PDO to access a MySQL database real prepared statements are not used by default. To fix this you have to disable the emulation of prepared statements. An example of creating a connection using PDO is:

$dbConnection = new PDO('mysql:dbname=dbtest;host=127.0.0.1;charset=utf8', 'user', 'password');

$dbConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

In the above example the error mode isn't strictly necessary, but it is advised to add it. This way the script will not stop with a Fatal Error when something goes wrong. And it gives the developer the chance to catch any error(s) which are thrown as PDOExceptions.

What is mandatory, however, is the first setAttribute() line, which tells PDO to disable emulated prepared statements and use real prepared statements. This makes sure the statement and the values aren't parsed by PHP before sending it to the MySQL server (giving a possible attacker no chance to inject malicious SQL).

Although you can set the charset in the options of the constructor, it's important to note that 'older' versions of PHP (before 5.3.6) silently ignored the charset parameter in the DSN.

Explanation

The SQL statement you pass to prepare is parsed and compiled by the database server. By specifying parameters (either a ? or a named parameter like :name in the example above) you tell the database engine where you want to filter on. Then when you call execute, the prepared statement is combined with the parameter values you specify.

The important thing here is that the parameter values are combined with the compiled statement, not an SQL string. SQL injection works by tricking the script into including malicious strings when it creates SQL to send to the database. So by sending the actual SQL separately from the parameters, you limit the risk of ending up with something you didn't intend.

Any parameters you send when using a prepared statement will just be treated as strings (although the database engine may do some optimization so parameters may end up as numbers too, of course). In the example above, if the $name variable contains 'Sarah'; DELETE FROM employees the result would simply be a search for the string "'Sarah'; DELETE FROM employees", and you will not end up with an empty table.

Another benefit of using prepared statements is that if you execute the same statement many times in the same session it will only be parsed and compiled once, giving you some speed gains.

Oh, and since you asked about how to do it for an insert, here's an example (using PDO):

$preparedStatement = $db->prepare('INSERT INTO table (column) VALUES (:column)');

$preparedStatement->execute([ 'column' => $unsafeValue ]);

Can prepared statements be used for dynamic queries?

While you can still use prepared statements for the query parameters, the structure of the dynamic query itself cannot be parametrized and certain query features cannot be parametrized.

For these specific scenarios, the best thing to do is use a whitelist filter that restricts the possible values.

// Value whitelist
// $dir can only be 'DESC', otherwise it will be 'ASC'
if (empty($dir) || $dir !== 'DESC') {
   $dir = 'ASC';
}

I'll start of by linking to the manual and then going into what I've seen and heard in the field.

Organizing phpunit test suites

Module / Test folder organization in the file system

My recommended approach is combining the file system with an xml config.

tests/
 \ unit/
 | - module1
 | - module2
 - integration/
 - functional/

with a phpunit.xml with a simple:

<testsuites>
  <testsuite name="My whole project">
    <directory>tests</directory>
  </testsuite>
</testsuites>

you can split the testsuites if you want to but thats a project to project choice.

Running phpunit will then execute ALL tests and running phpunit tests/unit/module1 will run all tests of module1.

Organization of the "unit" folder

The most common approach here is to mirror your source/ directory structure in your tests/unit/ folder structure.

You have one TestClass per ProductionClass anyways so it's a good approach in my book.

In file organization

• One class per file.

It's not going to work anyways if you have more than one test class in one file so avoid that pitfall.

• Don't have a test namespace

It just makes writing the test more verbose as you need an additional use statement so I'd say the testClass should go in the same namespace as the production class but that is nothing PHPUnit forces you to do. I've just found it to be easier with no drawbacks.

Executing only a few tests

For example phpunit --filter Factory executes all FactoryTests while phpunit tests/unit/logger/ executes everything logging related.

You can use @group tags for something like issue numbers, stories or something but for "modules" I'd use the folder layout.

Multiple xml files

It can be useful to create multiple xml files if you want to have:

• one without code coverage
• one just for the unit tests (but not for the functional or integration or long running tests)
• other common "filter" cases
• PHPBB3 for example does that for their phpunit.xmls

Code coverage for your tests

As it is related to starting a new project with tests:

• My suggestion is to use @covers tags like described in my blog (Only for unit tests, always cover all non public functions, always use covers tags.
• Don't generate coverage for your integration tests. It gives you a false sense of security.
• Always use whitelisting to include all of your production code so the numbers don't lie to you!

Autoloading and bootstrapping your tests

You don't need any sort of auto loading for your tests. PHPUnit will take care of that.

Use the <phpunit bootstrap="file"> attribute to specify your test bootstrap. tests/bootstrap.php is a nice place to put it. There you can set up your applications autoloader and so on (or call your applications bootstrap for that matter).

Summary

• Use the xml configuration for pretty much everything
• Seperate unit and integration tests
• Your unit test folders should mirror your applications folder structure
• To only execute specif tests use phpunit --filter or phpunit tests/unit/module1
• Use the strict mode from the get go and never turn it off.

Sample projects to look at

• Sebastian Bergmanns "Bank Account" example project
• phpBB3 Even so they have to fight some with their legacy ;)
• Symfony2
• Doctrine2