Add mix mneme.watch (#83)

Closes #82.

.tool-versions

@@ -1,2 +1,2 @@
-elixir 1.17.1-otp-27
-erlang 27.0
+elixir 1.17.2-otp-26
+erlang 26.2.5.2

README.md

@@ -38,6 +38,7 @@ But, unlike ordinary tests, Mneme asks if you'd like the test updated for the ne
   * **Seamless integration with ExUnit:** no need to change your workflow, just run `mix test`.
   * **Interactive prompts in your terminal** when a new assertion is added or an existing one changes.
   * **Syntax-aware diffs** highlight the meaningful changes in a value.
+  * **Built-in test watcher:** see changes immediately with `mix mneme.watch`.
 
 ## Interactive tour
 
@@ -62,7 +63,21 @@ $ elixir tour_mneme.exs
     end
     ```
 
-2.  Add `:mneme` to your `:import_deps` in `.formatter.exs`:
+2.  Add a `:preferred_cli_env` entry for `mix mneme.watch` in `mix.exs`:
+
+    ```elixir
+    def project do
+      [
+        ...
+        preferred_cli_env: [
+          "mneme.watch": :test
+        ],
+        ...
+      ]
+    end
+    ```
+
+3.  Add `:mneme` to your `:import_deps` in `.formatter.exs`:
 
     ```elixir
     [
@@ -71,14 +86,14 @@ $ elixir tour_mneme.exs
     ]
     ```
 
-3.  Start Mneme right after you start ExUnit in `test/test_helper.exs`:
+4.  Start Mneme right after you start ExUnit in `test/test_helper.exs`:
 
     ```elixir
     ExUnit.start()
     Mneme.start()
     ```
 
-4.  Add `use Mneme` wherever you `use ExUnit.Case`:
+5.  Add `use Mneme` wherever you `use ExUnit.Case`:
 
     ```elixir
     defmodule MyTest do
@@ -91,7 +106,7 @@ $ elixir tour_mneme.exs
     end
     ```
 
-5.  Run `mix test` and type `y<ENTER>` when prompted; your test should look like:
+6.  Run `mix test` and type `y<ENTER>` when prompted; your test should look like:
 
     ```elixir
     defmodule MyTest do

examples/demo_project/lib/lrcp_correct.ex → examples/demo_project/lib/lrcp.ex

@@ -1,4 +1,10 @@
-defmodule LRCPCorrect do
+defmodule LRCP do
+  @moduledoc """
+  Parser for the ficticious Protohackers "Line Reversal Control Protocol".
+
+  For more, see here: https://protohackers.com/problem/7
+  """
+
   def parse("/data/" <> rest) do
     with {:ok, session, rest} <- parse_integer(rest),
          {:ok, position, rest} <- parse_integer(rest),
@@ -11,9 +17,8 @@ defmodule LRCPCorrect do
   end
 
   def parse("/connect/" <> rest) do
-    with {:ok, session, ""} <- parse_integer(rest) do
-      {:ok, {:connect, session: session}}
-    else
+    case parse_integer(rest) do
+      {:ok, session, ""} -> {:ok, {:connect, session: session}}
       {:ok, _, rest} -> {:error, rest}
       error -> error
     end
@@ -30,9 +35,8 @@ defmodule LRCPCorrect do
   end
 
   def parse("/close/" <> rest) do
-    with {:ok, session, ""} <- parse_integer(rest) do
-      {:ok, {:close, session: session}}
-    else
+    case parse_integer(rest) do
+      {:ok, session, ""} -> {:ok, {:close, session: session}}
       {:ok, _, rest} -> {:error, rest}
       error -> error
     end

examples/demo_project/test/lrcp_test.exs

@@ -3,8 +3,6 @@ defmodule LRCPTest do
   use Mneme, dry_run: true
 
   describe "parse/1" do
-    alias LRCPCorrect, as: LRCP
-
     @tag :first_example
     test "parses valid messages (1)" do
       auto_assert LRCP.parse("/connect/12345/")

lib/mix/tasks/mneme.watch.ex

@@ -0,0 +1,59 @@
+defmodule Mix.Tasks.Mneme.Watch do
+  @shortdoc "Run tests when files change"
+  @moduledoc """
+  Runs the tests for a project when source files change.
+
+  This task is similar to [`mix test.watch`](https://hex.pm/packages/mix_test_watch),
+  but updated to work with Mneme:
+
+    * interrupts Mneme prompts, saving already-accepted changes
+    * doesn't re-trigger when test files are updated by Mneme
+
+  ## Setup
+
+  To ensure `mix mneme.watch` runs in the test environment, add a
+  `:preferred_cli_env` entry in `mix.exs`:
+
+      def project do
+        [
+          ...
+          preferred_cli_env: [
+            "mneme.watch": :test
+          ],
+          ...
+        ]
+      end
+
+  ## Command line options
+
+  This task runs `mix test` under the hood and passes all CLI arguments
+  to it directly. For instance:
+
+  ```sh
+  # only run tests tagged with `some_tag: true`
+  $ mix mneme.watch --only some_tag
+
+  # only run tests from one file
+  $ mix mneme.watch test/my_app/my_test.exs
+  ```
+
+  See the `mix test` documentation for more information.
+  """
+
+  use Mix.Task
+
+  @doc false
+  @impl Mix.Task
+  @spec run([String.t()]) :: no_return()
+  def run(args) do
+    Mix.env(:test)
+
+    children = [
+      {Mneme.Watch.TestRunner, cli_args: args}
+    ]
+
+    Supervisor.start_link(children, strategy: :one_for_one)
+
+    :timer.sleep(:infinity)
+  end
+end

lib/mneme/assertion.ex

@@ -253,6 +253,10 @@ defmodule Mneme.Assertion do
     raise Mneme.InternalError, original_error: error, original_stacktrace: stacktrace
   end
 
+  defp handle_assertion({:error, {:internal, error}}, _, _, _) do
+    raise Mneme.InternalError, original_error: error, original_stacktrace: []
+  end
+
   defp eval(%{value: value, context: ctx} = assertion, env) do
     binding = [{{:value, :mneme}, value} | ctx.binding]
 

lib/mneme/patcher.ex

@@ -38,6 +38,10 @@ defmodule Mneme.Patcher do
   """
   @spec finalize!(state) :: :ok | {:error, term()}
   def finalize!(project) do
+    project
+    |> Rewrite.paths()
+    |> Mneme.Watch.TestRunner.notify_about_to_save()
+
     case Rewrite.write_all(project) do
       {:ok, _project} ->
         :ok
@@ -61,7 +65,7 @@ defmodule Mneme.Patcher do
 
     case prepare_assertion(assertion, project) do
       {:ok, {assertion, node}} ->
-        patch!(project, assertion, counter, node)
+        prompt_and_patch!(project, assertion, counter, node)
 
       {:error, :not_found} ->
         {{:error, :file_changed}, project}
@@ -71,11 +75,7 @@ defmodule Mneme.Patcher do
       {{:error, {:internal, error, __STACKTRACE__}}, project}
   end
 
-  defp patch!(_, %{value: :__mneme__super_secret_test_value_goes_boom__}, _, _) do
-    raise ArgumentError, "I told you!"
-  end
-
-  defp patch!(project, assertion, counter, node) do
+  defp prompt_and_patch!(project, assertion, counter, node) do
     case prompt_change(assertion, counter) do
       :accept ->
         ast = replace_assertion_node(node, assertion.code)
@@ -100,7 +100,7 @@ defmodule Mneme.Patcher do
         {{:error, :skipped}, project}
 
       select ->
-        patch!(project, Assertion.select(assertion, select), counter, node)
+        prompt_and_patch!(project, Assertion.select(assertion, select), counter, node)
     end
   end