Add network service assertion helpers

[emdobrin]

Task description

For the test NetworkService update the workflow for integration testing, similar to the iOS implementation:

• the setup step overwrites the network service; functional vs integration tests make the corresponding setup
• each test can set expected requests, and assert on network requests sent out, response connections
• reuse existing helpers for functional tests (FunctionalTestNetworkService)

Additional implementation details or code snippet(s)

No response