Only call compile_path when we effectively need it mix test, closes #4783

Author: José Valim

lib/mix/lib/mix/compilers/test.ex

@@ -21,12 +21,12 @@ defmodule Mix.Compilers.Test do
   It expects all of the test patterns, the test files that were matched for the
   test patterns, the test paths, and the opts from the test task.
   """
-  def require_and_run(test_patterns, matched_test_files, test_paths, compile_path, opts) do
+  def require_and_run(test_patterns, matched_test_files, test_paths, opts) do
     stale = opts[:stale]
 
     {test_files_to_run, stale_manifest_pid, parallel_require_callbacks} =
       if stale do
-        set_up_stale(matched_test_files, test_paths, compile_path, opts)
+        set_up_stale(matched_test_files, test_paths, opts)
       else
         {matched_test_files, nil, []}
       end
@@ -58,7 +58,7 @@ defmodule Mix.Compilers.Test do
     end
   end
 
-  defp set_up_stale(matched_test_files, test_paths, compile_path, opts) do
+  defp set_up_stale(matched_test_files, test_paths, opts) do
     manifest = manifest()
     modified = Mix.Utils.last_modified(manifest)
     all_sources = read_manifest()
@@ -95,20 +95,17 @@ defmodule Mix.Compilers.Test do
 
     test_files_to_run =
       sources
-      |> tests_with_changed_references(compile_path)
+      |> tests_with_changed_references()
       |> MapSet.union(stale)
       |> MapSet.to_list()
 
     if test_files_to_run == [] do
       write_manifest(sources)
-
       {[], nil, nil}
     else
       {:ok, pid} = Agent.start_link(fn -> sources end)
-
       cwd = File.cwd!()
       parallel_require_callbacks = [each_module: &each_module(pid, cwd, &1, &2, &3)]
-
       {test_files_to_run, pid, parallel_require_callbacks}
     end
   end
@@ -191,13 +188,13 @@ defmodule Mix.Compilers.Test do
 
   ## Test changed dependency resolution
 
-  defp tests_with_changed_references(test_sources, compile_path) do
+  defp tests_with_changed_references(test_sources) do
     test_manifest = manifest()
     [elixir_manifest] = Mix.Tasks.Compile.Elixir.manifests()
 
     if Mix.Utils.stale?([elixir_manifest], [test_manifest]) do
       elixir_manifest_entries =
-        CE.read_manifest(elixir_manifest, compile_path)
+        CE.read_manifest(elixir_manifest, Mix.Project.compile_path())
         |> Enum.group_by(&elem(&1, 0))
 
       stale_modules =

lib/mix/lib/mix/tasks/test.ex

@@ -184,11 +184,12 @@ defmodule Mix.Tasks.Test do
     end
 
     project = Mix.Project.config
-    compile_path = Mix.Project.compile_path(project)
+    
 
     # Start cover after we load deps but before we start the app.
     cover =
       if opts[:cover] do
+        compile_path = Mix.Project.compile_path(project)
         cover = Keyword.merge(@cover, project[:test_coverage] || [])
         cover[:tool].start(compile_path, cover)
       end
@@ -227,7 +228,7 @@ defmodule Mix.Tasks.Test do
 
     display_warn_test_pattern(matched_warn_test_files, test_pattern)
 
-    case CT.require_and_run(files, matched_test_files, test_paths, compile_path, opts) do
+    case CT.require_and_run(files, matched_test_files, test_paths, opts) do
       {:ok, %{failures: failures}} ->
         cover && cover.()