phpunit mock method multiple calls with different arguments

It’s not ideal to use at() if you can avoid it because as their docs claim

The $index parameter for the at() matcher refers to the index, starting at zero, in all method invocations for a given mock object. Exercise caution when using this matcher as it can lead to brittle tests which are too closely tied to specific implementation details.

Since 4.1 you can use withConsecutive eg.

$mock->expects($this->exactly(2))
     ->method('set')
     ->withConsecutive(
         [$this->equalTo('foo'), $this->greaterThan(0)],
         [$this->equalTo('bar'), $this->greaterThan(0)]
       );

If you want to make it return on consecutive calls:

  $mock->method('set')
         ->withConsecutive([$argA1, $argA2], [$argB1], [$argC1, $argC2])
         ->willReturnOnConsecutiveCalls($retValueA, $retValueB, $retValueC);