I have been writing lots of tests for services and framework/toolkit type components over the last year. In both of these areas of development, I have written unit and integration tests that use WCF calls over SSL. Using SSL means that certificates are required. While an x509 certificate can be loaded from a file path, most implementations that use certificates rely on the certificate already being imported into a certificate store on the local machine. This means that the environment in which the tests are executed needs to be configured prior to running the tests.
This scenario limits flexibility for two reasons. Firstly, another developer can’t get the solution from source control and simply run the tests as they won’t have the required certificate installed. Secondly, a continuous build process will not be able to build the solution on a build machine that hasn’t already been configured.