Allow the with_setup loader to receive no files

This use case has appeared more frequently, deserves this refactor.

test/lib/zeitwerk/test_eager_load_dir.rb

@@ -279,7 +279,7 @@ class TestEagerLoadDir < LoaderTest
   end
 
   test "shortcircuits if eager loaded" do
-    with_setup([]) do
+    with_setup do
       loader.eager_load
 
       # Dirty way to prove we shortcircuit.
@@ -298,14 +298,14 @@ def loader.actual_eager_load_dir(*)
   end
 
   test "raises Zeitwerk::Error if the argument is not a directory" do
-    with_setup([]) do
+    with_setup do
       e = assert_raises(Zeitwerk::Error) { loader.eager_load_dir(__FILE__) }
       assert_equal "#{__FILE__} is not a directory", e.message
     end
   end
 
   test "raises if the argument is not managed by the loader" do
-    with_setup([]) do
+    with_setup do
       e = assert_raises(Zeitwerk::Error) { loader.eager_load_dir(__dir__) }
       assert_equal "I do not manage #{__dir__}", e.message
     end

test/lib/zeitwerk/test_eager_load_namespace.rb

@@ -11,7 +11,7 @@ class TestEagerLoadNamespaceWithObjectRootNamespace < LoaderTest
   end
 
   test "shortcircuits if eager loaded" do
-    with_setup([]) do
+    with_setup do
       loader.eager_load
 
       # Dirty way to prove we shortcircuit.
@@ -166,7 +166,7 @@ def loader.actual_eager_load_dir(*)
   end
 
   test "raises if the argument is not a class or module object" do
-    with_setup([]) do
+    with_setup do
       e = assert_raises(Zeitwerk::Error) do
         loader.eager_load_namespace(self.class.name)
       end
@@ -175,7 +175,7 @@ def loader.actual_eager_load_dir(*)
   end
 
   test "raises if the argument is not a class or module object, even if eager loaded" do
-    with_setup([]) do
+    with_setup do
       loader.eager_load
       e = assert_raises(Zeitwerk::Error) do
         loader.eager_load_namespace(self.class.name)

test/lib/zeitwerk/test_load_file.rb

@@ -62,7 +62,7 @@ class TestLoadFile < LoaderTest
 
 class TestLoadFileErrors < LoaderTest
   test "raises if the argument does not exist" do
-    with_setup([]) do
+    with_setup do
       e = assert_raises { loader.load_file("foo.rb") }
       assert_equal "#{File.expand_path('foo.rb')} does not exist", e.message
     end

test/lib/zeitwerk/test_logging.rb

@@ -181,15 +181,15 @@ def logger.debug(message)
   end
 
   test "logs when eager loading starts" do
-    with_setup([]) do
+    with_setup do
       assert_logged(/eager load start/) do
         loader.eager_load
       end
     end
   end
 
   test "logs when eager loading ends" do
-    with_setup([]) do
+    with_setup do
       assert_logged(/eager load end/) do
         loader.eager_load
       end

test/support/loader_test.rb

@@ -79,7 +79,7 @@ def with_load_path(dirs = loader.dirs)
     dirs.each { |dir| $LOAD_PATH.delete(dir) }
   end
 
-  def with_setup(files, dirs: ".", namespace: Object, load_path: nil, rm: true)
+  def with_setup(files = [], dirs: ".", namespace: Object, load_path: nil, rm: true)
     with_files(files, rm: rm) do
       Array(dirs).each { |dir| loader.push_dir(dir, namespace: namespace) }
       loader.setup