diff --git a/pipreqs/pipreqs.py b/pipreqs/pipreqs.py
index 8182115..a84f39b 100644
--- a/pipreqs/pipreqs.py
+++ b/pipreqs/pipreqs.py
@@ -149,10 +149,6 @@ def get_all_imports(
     return list(packages - data)
 
 
-def filter_line(line):
-    return len(line) > 0 and line[0] != "#"
-
-
 def generate_requirements_file(path, imports, symbol):
     with _open(path, "w") as out_file:
         logging.debug('Writing {num} requirements: {imports} to {file}'.format(
@@ -319,7 +315,7 @@ def parse_requirements(file_):
         OSerror: If there's any issues accessing the file.
 
     Returns:
-        tuple: The contents of the file, excluding comments.
+        list: The contents of the file, excluding comments.
     """
     modules = []
     # For the dependency identifier specification, see
@@ -357,7 +353,6 @@ def parse_requirements(file_):
 
     return modules
 
-
 def compare_modules(file_, imports):
     """Compare modules in a file to imported modules in a project.
 
@@ -366,8 +361,8 @@ def compare_modules(file_, imports):
         imports (tuple): Modules being imported in the project.
 
     Returns:
-        tuple: The modules not imported in the project, but do exist in the
-               specified file.
+        set: The modules not imported in the project, but do exist in the
+            specified file.
     """
     modules = parse_requirements(file_)
 
diff --git a/tests/_data/imports.txt b/tests/_data/imports.txt
index 7180017..32eea8a 100644
--- a/tests/_data/imports.txt
+++ b/tests/_data/imports.txt
@@ -1,3 +1,3 @@
-pandas==2.0.0
-numpy>=1.2.3
+pandas==2.0.0
+numpy>=1.2.3
 torch<4.0.0
\ No newline at end of file
diff --git a/tests/test_pipreqs.py b/tests/test_pipreqs.py
index 520766b..f239f07 100644
--- a/tests/test_pipreqs.py
+++ b/tests/test_pipreqs.py
@@ -66,8 +66,17 @@ def setUp(self):
 
         self.project_clean = os.path.join(os.path.dirname(__file__), "_data_clean")
         self.project_invalid = os.path.join(os.path.dirname(__file__), "_invalid_data")
+        self.parsed_packages = [
+            {"name": "pandas", "version": "2.0.0"},
+            {"name": "numpy", "version": "1.2.3"},
+            {"name": "torch", "version": "4.0.0"},
+        ]
+        self.empty_filepath = os.path.join(self.project, "empty.txt")
+        self.imports_filepath = os.path.join(self.project, "imports.txt")
+
         self.project_with_ignore_directory = os.path.join(os.path.dirname(__file__), "_data_ignore")
         self.project_with_duplicated_deps = os.path.join(os.path.dirname(__file__), "_data_duplicated_deps")
+        
         self.requirements_path = os.path.join(self.project, "requirements.txt")
         self.alt_requirement_path = os.path.join(self.project, "requirements2.txt")
 
@@ -438,6 +447,31 @@ def test_clean_with_imports_to_clean(self):
             data = f.read().lower()
             self.assertTrue(cleaned_module not in data)
 
+    def test_compare_modules(self):
+        test_cases = [
+            (self.empty_filepath, [], set()),  # both empty
+            (self.empty_filepath, self.parsed_packages, set()),  # only file empty
+            (
+                self.imports_filepath,
+                [],
+                set(package["name"] for package in self.parsed_packages),
+            ),  # only imports empty
+            (self.imports_filepath, self.parsed_packages, set()),  # no difference
+            (
+                self.imports_filepath,
+                self.parsed_packages[1:],
+                set([self.parsed_packages[0]["name"]]),
+            ),  # common case
+        ]
+
+        for test_case in test_cases:
+            with self.subTest(test_case):
+                filename, imports, expected_modules_not_imported = test_case
+
+                modules_not_imported = pipreqs.compare_modules(filename, imports)
+
+                self.assertSetEqual(modules_not_imported, expected_modules_not_imported)
+                
     def test_output_requirements(self):
         """
         Test --print parameter