MockGRPC
v0.2.0

View Source Integrating with ConnGRPC

simulating-unavailable-channel

 Simulating unavailable channel

To make MockGRPC.up/0 and MockGRPC.down/0 work with ConnGRPC, you can use its mock option.

First, add to your test configuration file (e.g. config/test.exs):

Application.put_env(:demo, :conn_grpc_adapter, MockGRPC.Adapter)

Application.put_env(:demo, :conn_grpc_mock, fn test_pid ->
  MockGRPC.set_context(test_pid)
  GRPC.Stub.connect("dummy", adapter: MockGRPC.Adapter)
end)

Then, pass mock to your channel configuration.

If you're using ConnGRPC.Pool:

defmodule DemoPool do
  use ConnGRPC.Pool,
    pool_size: 5,
    channel: [
      address: Application.get_env(:demo, :demo_grpc_address),
      opts: [adapter: Application.get_env(:demo, :conn_grpc_adapter)],
      mock: Application.get_env(:demo, :conn_grpc_mock)
    ]
end

If you're using ConnGRPC.Channel:

defmodule DemoChannel do
  use ConnGRPC.Channel,
    address: Application.get_env(:demo, :demo_grpc_address),
    opts: [adapter: Application.get_env(:demo, :conn_grpc_adapter)],
    mock: Application.get_env(:demo, :conn_grpc_mock),
end

why-this-is-needed

 Why this is needed

ConnGRPC starts a channel, or a pool of channels, to be reused throughout your app, and these channels are started as part of your application supervision tree. Because of this global nature, by default it's not possible to test connection failure in isolation in parallel tests.

Turning the channel down would do it for the entire application, and prevent parallel tests from testing different scenarios where the channel is up.

To overcome that, ConnGRPC allows passing a mock function on the channel setup, so that you can overwrite the channel returned by it. You can then integrate that mock function with MockGRPC.set_context/1 and call GRPC.Stub.connect/2 inside it to return the mocked channel in an isolated manner.