Improve MakefileInstaller: only run 'make install' if an install target exists

- Added parsing of Makefile to detect real 'install' target
- Added safe fallback when Makefile cannot be read
- Added informative skip message when install target is missing
- Updated unit tests to cover: install present, install missing, file read
- Removed circular self-import causing test import failures

Conversation reference: https://chatgpt.com/share/6936a2bf-6aa4-800f-a1bc-7c8eac66bc18

tests/unit/pkgmgr/installers/test_makefile_installer.py

@@ -2,7 +2,7 @@
 
 import os
 import unittest
-from unittest.mock import patch
+from unittest.mock import patch, mock_open
 
 from pkgmgr.context import RepoContext
 from pkgmgr.installers.makefile import MakefileInstaller
@@ -36,9 +36,25 @@ class TestMakefileInstaller(unittest.TestCase):
         self.assertFalse(self.installer.supports(self.ctx))
 
     @patch("pkgmgr.installers.makefile.run_command")
+    @patch(
+        "builtins.open",
+        new_callable=mock_open,
+        read_data="install:\n\t@echo 'installing'\n",
+    )
     @patch("os.path.exists", return_value=True)
-    def test_run_executes_make_install(self, mock_exists, mock_run_command):
+    def test_run_executes_make_install_when_target_present(
+        self, mock_exists, mock_file, mock_run_command
+    ):
         self.installer.run(self.ctx)
+
+        # Ensure we checked the Makefile and then called make install.
+        mock_file.assert_called_once_with(
+            os.path.join(self.ctx.repo_dir, "Makefile"),
+            "r",
+            encoding="utf-8",
+            errors="ignore",
+        )
+
         cmd = mock_run_command.call_args[0][0]
         self.assertEqual(cmd, "make install")
         self.assertEqual(
@@ -46,6 +62,27 @@ class TestMakefileInstaller(unittest.TestCase):
             self.ctx.repo_dir,
         )
 
+    @patch("pkgmgr.installers.makefile.run_command")
+    @patch(
+        "builtins.open",
+        new_callable=mock_open,
+        read_data="all:\n\t@echo 'nothing here'\n",
+    )
+    @patch("os.path.exists", return_value=True)
+    def test_run_skips_when_no_install_target(
+        self, mock_exists, mock_file, mock_run_command
+    ):
+        self.installer.run(self.ctx)
+
+        # We should have read the Makefile, but not called run_command().
+        mock_file.assert_called_once_with(
+            os.path.join(self.ctx.repo_dir, "Makefile"),
+            "r",
+            encoding="utf-8",
+            errors="ignore",
+        )
+        mock_run_command.assert_not_called()
+
 
 if __name__ == "__main__":
     unittest.main()