Mocking Demeter Chains And Fluent Interfaces

Both of these terms refer to the growing practice of invoking statements similar to:

$object->foo()->bar()->zebra()->alpha()->selfDestruct();

The long chain of method calls isn’t necessarily a bad thing, assuming they each link back to a local object the calling class knows. Just as a fun example, Mockery’s long chains (after the first shouldReceive() method) all call to the same instance of \Mockery\Expectation. However, sometimes this is not the case and the chain is constantly crossing object boundaries.

In either case, mocking such a chain can be a horrible task. To make it easier Mockery support demeter chain mocking. Essentially, we shortcut through the chain and return a defined value from the final call. For example, let’s assume selfDestruct() returns the string “Ten!” to $object (an instance of CaptainsConsole). Here’s how we could mock it.

$mock = \Mockery::mock('CaptainsConsole');
$mock->shouldReceive('foo->bar->zebra->alpha->selfDestruct')->andReturn('Ten!');

The above expectation can follow any previously seen format or expectation, except that the method name is simply the string of all expected chain calls separated by ->. Mockery will automatically setup the chain of expected calls with its final return values, regardless of whatever intermediary object might be used in the real implementation.

Arguments to all members of the chain (except the final call) are ignored in this process.