Generate code required to mock Erlang modules

Author: pmeinhardt

lib/sshkit/connection.ex

@@ -5,7 +5,7 @@ defmodule SSHKit.Connection do
   A connection struct has the following fields:
 
   * `host` - the name or IP of the remote host
-  * `port` - the port to connect to
+  * `port` - the port connected to
   * `options` - additional connection options
   * `ref` - the underlying `:ssh` connection ref
   """

test/support/functional_case.ex

@@ -17,7 +17,9 @@ defmodule SSHKit.FunctionalCase do
       @moduletag :functional
 
       setup do
-        # Stub mocks with implementations delegating to the proper Erlang modules
+        # Stub mocks with implementations delegating to the original Erlang
+        # modules, essentially "unmocking" them unless explicit expectations
+        # are set up.
         Mox.stub_with(MockErlangSsh, ErlangSsh)
         Mox.stub_with(MockErlangSshConnection, ErlangSshConnection)
         Mox.stub_with(MockErlangSshSftp, ErlangSshSftp)

test/support/gen.ex

@@ -0,0 +1,61 @@
+defmodule Gen do
+  @moduledoc false
+
+  @doc """
+  Generates a behaviour based on an existing module.
+
+  Mox requires a behaviour to be defined in order to create a mock. To mock
+  core modules in tests - e.g. :ssh, :ssh_connection and :ssh_sftp - we need
+  behaviours mirroring their public API.
+  """
+  def defbehaviour(name, target) when is_atom(name) and is_atom(target) do
+    info = moduledoc("Generated behaviour for #{inspect(target)}.")
+
+    body =
+      for {fun, arity} <- functions(target) do
+        args = 0..arity |> Enum.map(fn _ -> {:term, [], []} end) |> tl()
+
+        quote do
+          @callback unquote(fun)(unquote_splicing(args)) :: term()
+        end
+      end
+
+    Module.create(name, info ++ body, Macro.Env.location(__ENV__))
+  end
+
+  @doc """
+  Generates a module delegating all function calls to another module.
+
+  Mox requires modules used for stubbing to implement the mocked behaviour. To
+  mock core modules without behaviour definitions, we generate stand-in modules
+  which delegate
+  """
+  def defdelegated(name, target, options \\ [])
+      when is_atom(name) and is_atom(target) and is_list(options) do
+    info =
+      moduledoc("Generated stand-in module for #{inspect(target)}.") ++
+        behaviour(Keyword.get(options, :behaviour))
+
+    body =
+      for {fun, arity} <- functions(target) do
+        args = Macro.generate_arguments(arity, name)
+
+        quote do
+          defdelegate unquote(fun)(unquote_splicing(args)), to: unquote(target)
+        end
+      end
+
+    Module.create(name, info ++ body, Macro.Env.location(__ENV__))
+  end
+
+  defp functions(module) do
+    exports = module.module_info(:exports)
+    Keyword.drop(exports, ~w[__info__ module_info]a)
+  end
+
+  defp moduledoc(nil), do: []
+  defp moduledoc(docstr), do: [quote(do: @moduledoc(unquote(docstr)))]
+
+  defp behaviour(nil), do: []
+  defp behaviour(name), do: [quote(do: @behaviour(unquote(name)))]
+end

test/support/mocks.ex

@@ -1,79 +1,13 @@
-defmodule ErlangSshBehaviour do
-  @moduledoc false
+require Gen
 
-  @type conn() :: term()
+Gen.defbehaviour(ErlangSsh.Behaviour, :ssh)
+Gen.defdelegated(ErlangSsh, :ssh, behaviour: ErlangSsh.Behaviour)
+Mox.defmock(MockErlangSsh, for: ErlangSsh.Behaviour)
 
-  @callback connect(binary(), integer(), keyword(), timeout()) :: {:ok, conn()} | {:error, term()}
-  @callback close(conn()) :: :ok
-end
+Gen.defbehaviour(ErlangSshConnection.Behaviour, :ssh_connection)
+Gen.defdelegated(ErlangSshConnection, :ssh_connection, behaviour: ErlangSshConnection.Behaviour)
+Mox.defmock(MockErlangSshConnection, for: ErlangSshConnection.Behaviour)
 
-defmodule ErlangSsh do
-  @moduledoc false
-
-  @behaviour ErlangSshBehaviour
-
-  defdelegate connect(host, port, options, timeout), to: :ssh
-  defdelegate close(conn), to: :ssh
-end
-
-Mox.defmock(MockErlangSsh, for: ErlangSshBehaviour)
-
-defmodule ErlangSshConnectionBehaviour do
-  @moduledoc false
-
-  @type conn() :: term()
-  @type chan() :: integer()
-
-  @callback session_channel(conn(), integer(), integer(), timeout()) ::
-              {:ok, chan()} | {:error, term()}
-  @callback subsystem(conn(), chan(), charlist(), timeout()) ::
-              :success | :failure | {:error, :timeout} | {:error, :closed}
-  @callback close(conn(), chan()) :: :ok
-  @callback exec(conn(), chan(), binary(), timeout()) ::
-              :success | :failure | {:error, :timeout} | {:error, :closed}
-  @callback ptty_alloc(conn(), chan(), keyword(), timeout()) ::
-              :success | :failure | {:error, :timeout} | {:error, :closed}
-  @callback send(conn(), chan(), 0..1, binary(), timeout()) ::
-              :ok | {:error, :timeout} | {:error, :closed}
-  @callback send_eof(conn(), chan()) :: :ok | {:error, :closed}
-  @callback adjust_window(conn(), chan(), integer()) :: :ok
-end
-
-defmodule ErlangSshConnection do
-  @moduledoc false
-
-  @behaviour ErlangSshConnectionBehaviour
-
-  defdelegate session_channel(conn, initial_window_size, max_packet_size, timeout),
-    to: :ssh_connection
-
-  defdelegate subsystem(conn, chan, name, timeout), to: :ssh_connection
-  defdelegate close(conn, chan), to: :ssh_connection
-  defdelegate exec(conn, chan, command, timeout), to: :ssh_connection
-  defdelegate ptty_alloc(conn, chan, keyword, timeout), to: :ssh_connection
-  defdelegate send(conn, chan, type, data, timeout), to: :ssh_connection
-  defdelegate send_eof(conn, chan), to: :ssh_connection
-  defdelegate adjust_window(conn, chan, size), to: :ssh_connection
-end
-
-Mox.defmock(MockErlangSshConnection, for: ErlangSshConnectionBehaviour)
-
-defmodule ErlangSshSftpBehaviour do
-  @moduledoc false
-
-  @type conn() :: term()
-  @type chan() :: pid()
-
-  # TODO
-  @callback start_channel(conn(), keyword()) :: {:ok, chan()} | {:error, term()}
-end
-
-defmodule ErlangSshSftp do
-  @moduledoc false
-
-  @behaviour ErlangSshSftpBehaviour
-
-  defdelegate start_channel(conn, options), to: :ssh_sftp
-end
-
-Mox.defmock(MockErlangSshSftp, for: ErlangSshSftpBehaviour)
+Gen.defbehaviour(ErlangSshSftp.Behaviour, :ssh_sftp)
+Gen.defdelegated(ErlangSshSftp, :ssh_sftp, behaviour: ErlangSshSftp.Behaviour)
+Mox.defmock(MockErlangSshSftp, for: ErlangSshSftp.Behaviour)