diff --git a/config_root/config/config_utils.py b/config_root/config/config_utils.py
index e80753736..5594e70ec 100644
--- a/config_root/config/config_utils.py
+++ b/config_root/config/config_utils.py
@@ -12,9 +12,9 @@
 import re
 from typing import Any, Iterable, List, Optional
 
-import config_root.config.config_ as crococon
 import pandas as pd
 
+import config_root.config.config_ as crococon
 import helpers.hdbg as hdbg
 import helpers.hdict as hdict
 import helpers.hdocker as hdocker
@@ -86,7 +86,6 @@ def replace_shared_dir_paths(
     return new_config
 
 
-# TODO(gp): Add unit tests.
 def sort_config_string(txt: str) -> str:
     """
     Sort a string representing a Config in alphabetical order by the first
diff --git a/config_root/config/test/test_config.py b/config_root/config/test/test_config.py
index 88b093fa6..8a080813e 100644
--- a/config_root/config/test/test_config.py
+++ b/config_root/config/test/test_config.py
@@ -1864,7 +1864,6 @@ def test1(self) -> None:
         key2:
           key3:
             key4:
-
         """
         should_be_pickleable_before = True
         force_values_to_string = True
@@ -1886,7 +1885,6 @@ def test2(self) -> None:
         key2:
           key3:
             key4:
-
         """
         should_be_pickleable_before = False
         force_values_to_string = True
@@ -2085,7 +2083,6 @@ def test5(self) -> None:
     def test6(self) -> None:
         """
         Test debug mode with `marked_as_used` == True.
-
         This is a smoketest since the output of stacktrace is unstable.
         """
         # Set multiline string value.
@@ -2496,3 +2493,127 @@ def test3(self) -> None:
         key1 (marked_as_used=False, writer=None, val_type=str): hello.txt
         """
         self.execute_stmt(stmt, exp, mode, globals())
+
+
+# #############################################################################
+# TestSortConfigString
+# #############################################################################
+
+
+class TestSortConfigString(hunitest.TestCase):
+    """
+    Test sort_config_string function with various config formats.
+    """
+
+    def check_sort_test(self, txt: str, expected: str) -> None:
+        """
+        Helper method to test sorted config output.
+        """
+        result = cconfig.sort_config_string(txt)
+        self.assertEqual(result, expected, fuzzy_match=True)
+
+    def test1(self) -> None:
+        """
+        Test sorting of single-line config entries.
+        """
+        txt = """
+        z_config: value3
+        a_config: value1
+        m_config: value2
+        """
+        expected = """
+        a_config: value1
+        m_config: value2
+        z_config: value3
+        """
+        self.check_sort_test(txt, expected)
+
+    def test2(self) -> None:
+        """
+        Test sorting of multi-level config entries.
+        """
+        txt = """
+        build_model:
+          activation: sigmoid
+          layers: 3
+        build_data:
+          source: database
+          type: timeseries
+        """
+        expected = """
+        build_data:
+          source: database
+          type: timeseries
+        build_model:
+          activation: sigmoid
+          layers: 3
+        """
+        self.check_sort_test(txt, expected)
+
+    def test3(self) -> None:
+        """
+        Test handling of different indentation patterns and space combinations.
+        """
+        txt = """
+        config1:
+          normal_indent: value1
+         wrong_indent: value2
+        config2:
+            extra_indent: value3
+        single: value4
+         bad_indent: value5
+        """
+        expected = """
+        config1:
+          normal_indent: value1
+        config2:
+            extra_indent: value3
+        single value4
+        """
+        self.check_sort_test(txt, expected)
+
+    def test4(self) -> None:
+        """
+        Test sorting of complex nested structure with multiple levels.
+        """
+        txt = """
+        z_parent:
+          child2:
+            key1: val1
+            key2: val2
+          child1: value
+        a_parent:
+          nested:
+            deep:
+              key: value
+          simple: test
+        """
+        expected = """
+        a_parent:
+          nested:
+            deep:
+              key: value
+          simple: test
+        z_parent:
+          child1: value
+          child2:
+            key1: val1
+            key2: val2
+        """
+        self.check_sort_test(txt, expected)
+
+    def test5(self) -> None:
+        """
+        Test sorting with special characters in config names.
+        """
+        txt = """
+        _special: value
+        #comment: note
+        @config: test
+        """
+        expected = """
+        #comment: note
+        @config: test
+        _special: value
+        """
+        self.check_sort_test(txt, expected)