Test failures may be observed in a managed package when you run all tests in your organization. This is ordinary and expected with any managed package and can be safely ignored. Because managed package test failures can't always be prevented, Salesforce does not consider coverage levels or failures from other namespaces when deploying code. In other words, test failures and coverage in a managed package will not impact the deployment of other code or apps.
It is not possible to write unit tests that pass in all Salesforce organizations because such organizations can be customized in any number of ways including validation rules, workflow rules, and custom code. When deploying change sets in production, managed package tests will not run by default and, therefore, will not prevent code from deploying.