Xcode Unit Testing with Cocoapods

I had the same issue. I solved it by moving pod 'Firebase' to my test target. Change your Podfile to this:

platform :ios, '9.0'
use_frameworks!
inhibit_all_warnings!

target 'MyApp' do
    pod 'Firebase/Auth'
    pod 'Firebase/Database'
    pod 'Firebase/Storage'

    target 'MyAppTests' do
        inherit! :search_paths
        pod 'Firebase'
    end
end