Faulty dependency constraint affecting getObjectForTrait (failure using --prefer-lowest)

[Bilge]

Q	A
PHPUnit version	7.1.2
PHP version	7.1.6
Installation Method	Composer

A call to getObjectForTrait() works on PHPUnit 7.1.2, but fails when installing the same version with composer up --prefer-lowest. Following is the list of changed packages when prefer lowest is enabled.

$ composer up --prefer-lowest
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 1 install, 10 updates, 3 removals
  - Removing webmozart/assert (1.3.0)
  - Removing phpdocumentor/type-resolver (0.4.0)
  - Removing phpdocumentor/reflection-common (1.0.1)
  - Updating scriptfusion/retry (1.1.1 => 1.1.0): Loading from cache
  - Updating amphp/amp (v2.0.6 => v2.0.0): Loading from cache
  - Updating psr/cache (1.0.1 => 1.0.0): Loading from cache
  - Updating myclabs/deep-copy (1.7.0 => 1.6.1): Loading from cache
  - Updating doctrine/instantiator (1.1.0 => 1.0.5): Loading from cache
  - Installing dflydev/markdown (v1.0.0): Loading from cache
  - Updating phpdocumentor/reflection-docblock (4.3.0 => 2.0.0): Loading from cache
  - Updating phpspec/prophecy (1.7.5 => v1.7.0): Loading from cache
  - Updating phpunit/php-file-iterator (1.4.5 => 1.4.3): Loading from cache
  - Updating phpunit/php-code-coverage (6.0.3 => 6.0.1): Loading from cache
  - Updating phpunit/phpunit-mock-objects (6.1.1 => 6.1.0): Loading from cache
Package dflydev/markdown is abandoned, you should avoid using it. Use michelf/php-markdown instead.
Writing lock file
Generating autoload files

Overriding phpunit/phpunit-mock-objects with version ^6.1.1 fixes the issue.

• Here is the code used to reproduce the issue.
• Here is a Travis test run that verifies the issue.

[sebastianbergmann]

I understand what --prefer-lowest does but I do not understand why people use it, makes no sense to me. Why would you not want the latest version of a component that is compatible with the version of the component that is required?

Anyways, I merged your pull request.

[Bilge]

@sebastianbergmann Since you understand --prefer-lowest you should understand why I'm using it because my reasons are the same as yours. I do not use it for development, only for my Composer constraint testing. However, there is no way I know of to only test my own constraints are correct: it also requires all dependencies to be using the correct constraints also. That is why I recommended you take a look at your test coverage for getObjectForTrait(), because it seems you must have a blind spot there.