add unit test for "get_locally_installed_packages" function

tests/_local_packages/invalid_module/EGG-INFO/top_level.txt

@@ -0,0 +1 @@
+invalid_module

tests/_local_packages/invalid_package/top_level.txt

@@ -0,0 +1 @@
+tests

tests/_local_packages/valid_package-1.0.0.dist-info/top_level.txt

@@ -0,0 +1,2 @@
+valid_package
+tests

tests/test_pipreqs.py

@@ -9,6 +9,8 @@
 """
 
 import unittest
+from unittest.mock import patch
+import sys
 import os
 import requests
 
@@ -48,6 +50,10 @@ def setUp(self):
             self.project,
             "requirements2.txt"
             )
+        self.local_packages_path = os.path.join(
+            os.path.dirname(__file__),
+            "_local_packages"
+            )
 
     def test_get_all_imports(self):
         imports = pipreqs.get_all_imports(self.project)
@@ -109,6 +115,16 @@ def test_get_use_local_only(self):
         for item in imports_with_info:
             self.assertTrue(item['name'].lower() in self.local)
 
+    def test_get_locally_installed_packages(self):
+        with patch.object(sys, 'path', new=[self.local_packages_path]):
+            local_installed_packages = pipreqs.get_locally_installed_packages()
+            expected_output = [
+                {'exports': [], 'name': 'invalid_package', 'version': None},
+                {'exports': ['valid_package'], 'name': 'valid_package', 'version': '1.0.0'},
+                {'exports': [], 'name': 'EGG', 'version': 'INFO'}
+            ]
+            self.assertEqual(local_installed_packages, expected_output)
+
     def test_init(self):
         """
         Test that all modules we will test upon are in requirements file
@@ -145,7 +161,7 @@ def test_init_savepath(self):
         Test that we can save requirements.txt correctly
         to a different path
         """
-        pipreqs.init({'<path>': self.project, '--savepath': self.alt_requirement_path, 
+        pipreqs.init({'<path>': self.project, '--savepath': self.alt_requirement_path,
                       '--use-local': None, '--proxy':None, '--pypi-server':None,  '--print': False,
                       '--diff': None, '--clean': None, '--mode': None})
         assert os.path.exists(self.alt_requirement_path) == 1
@@ -163,7 +179,7 @@ def test_init_overwrite(self):
         """
         with open(self.requirements_path, "w") as f:
             f.write("should_not_be_overwritten")
-        pipreqs.init({'<path>': self.project, '--savepath': None, '--use-local': None, 
+        pipreqs.init({'<path>': self.project, '--savepath': None, '--use-local': None,
                       '--force': None, '--proxy':None, '--pypi-server':None, '--print': False,
                       '--diff': None, '--clean': None, '--mode': None})
         assert os.path.exists(self.requirements_path) == 1
@@ -203,7 +219,7 @@ def test_ignored_directory(self):
         Test --ignore parameter
         """
         pipreqs.init(
-            {'<path>': self.project_with_ignore_directory, '--savepath': None, 
+            {'<path>': self.project_with_ignore_directory, '--savepath': None,
                       '--print': False, '--use-local': None, '--force': True,
                       '--proxy':None, '--pypi-server':None,
                       '--ignore':'.ignored_dir,.ignore_second',
@@ -222,7 +238,7 @@ def test_dynamic_version_no_pin_scheme(self):
         Test --mode=no-pin
         """
         pipreqs.init(
-            {'<path>': self.project_with_ignore_directory, '--savepath': None, 
+            {'<path>': self.project_with_ignore_directory, '--savepath': None,
              '--print': False, '--use-local': None, '--force': True,
              '--proxy': None, '--pypi-server': None,
              '--diff': None,