composer.json

{
    "name": "codecollab/authentication",
    "description": "Authentication package of the CodeCollab project",
    "version": "0.1.0",
    "type": "library",
    "keywords": ["codecollab", "security", "authentication"],
    "homepage": "https://github.com/CodeCollab/Authentication",
    "license": "See the LICENSE file",
    "authors": [
        {
            "name": "Pieter Hordijk",
            "role": "Lead"
        }
    ],
    "autoload": {
        "psr-4": {"CodeCollab\\Authentication\\": "src/"}
    },
    "minimum-stability": "dev",
    "repositories": [
        {
            "type": "git",
            "url": "git@github.com:PeeHaa/phpunit-mock-objects.git"
        }
    ],
    "require": {
        "php": ">=7.0-dev",
        "codecollab/http": "dev-master"
    },
    "require-dev": {
        "phpunit/phpunit-mock-objects": "dev-fixes-seven as 3.0",
        "phpunit/phpunit": "^5"
    }
}

error

Loading composer repositories with package information
Reading composer.json of phpunit/phpunit-mock-objects (fix-blacklisted-methods-f
Reading composer.json of phpunit/phpunit-mock-objects (master)
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - The requested package phpunit/phpunit-mock-objects dev-fixes-seven as 3.0
could not be found.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your min
imum-stability setting
   see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> f
or more details.

Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further commo
n problems.