Php 如何查找冲突的编写器包？

我正试图在我将要创建的项目上更新PHPUnit版本。它有PHPUnit版本

~3.7

。当我运行

composer require phpunit/phpunit:~6--dev

时，它会打印出：

Problem 1
    - Can only install one of: phpunit/php-code-coverage[5.2.2, 1.2.18].
    - Can only install one of: phpunit/php-code-coverage[5.2.2, 1.2.18].
    - Can only install one of: phpunit/php-code-coverage[5.2.2, 1.2.18].
    - phpunit/phpunit 6.3.0 requires phpunit/php-code-coverage ^5.2.2 -> satisfiable by phpunit/php-code-coverage[5.2.2].
    - Installation request for phpunit/phpunit ^6.3 -> satisfiable by phpunit/phpunit[6.3.0].
    - Installation request for phpunit/php-code-coverage (locked at 1.2.18) -> satisfiable by phpunit/php-code-coverage[1.2.18].

然而，它不会说哪一个包是有问题的。编写器文件为

PS: 另外，为了以防万一，我运行了

composer require php:~7.1

，它成功了，但之后更新PHPUnit仍然不起作用。

需要使用

的包—使用依赖项更新

跑

更新
phpunit/phpunit
，同时更新其依赖项

见：


--使用依赖项更新：也更新新需要的包的依赖项

列出原因
如果这没用，就跑吧

$ composer why-not phpunit/phpunit:^6.0.0

列出无法安装程序包的原因

$ composer why-not phpunit/phpunit:^6.0.0