Had a bit of a think about how to do this:
Test the processor steps
So the first thing to do is make sure all your code logic is off loaded to a service or manager class. The processor class really should just be responsible for creating the service/manager class (by constructor injection of course :) ) and then calling the appropriate method.
So the main set of unit testing can be done for the individual functionality of the pipeline.
Test the processor
With the container now being a part of Sitecore in 8.2+, you can now test some processors directly. Pipelines now support the
resolve="true" attribute that will use the container to create the processor and inject any dependencies. So those are now testable. For processors that do not inject dependencies, you are back to FakeDb and mocking everything.
Test the pipeline
To test the pipeline as a whole and not have all the Sitecore binaries, config etc... (I agree, this isn't a great practice), we are going to have to write our own version of
CorePipeline.Run as a kind of test harness. That would then take the args and push them through the Process Method of each processor.
Initially - this sounds like it would be fairly simple to do, at a very basic level you could even do something as simple as:
public void TestMyPipeline()
var args = new Mock<ProcessorArgs>();
// TODO: populate the properites on the args mock
var processor1 = new Processor1(dependency1Mock.Object, dependency2Mock.Object);
var processor2 = new Processor1(dependency1Mock.Object, dependency2Mock.Object);
// Add your test assersions
But... ultimately, you still have the same problem. You need to mock or create any dependencies that get used in those processors and there is a lot to setup.
What is the best option?
For me - generally, unit testing each processor individually normally covers 99% of what is going to require testing. The extra overhead of running the entire pipeline gets into the rule of diminishing returns.
But you would have to evaluate how far you wanted to take the testing for your project.