[Concept,04/18] buildman: Add unit tests for print_func_size_detail()

diff --git a/tools/buildman/main.py b/tools/buildman/main.py
index 04993dcd87b..70547b2991d 100755
--- a/tools/buildman/main.py
+++ b/tools/buildman/main.py
@@ -39,6 +39,7 @@  def run_tests(skip_net_tests, debug, verbose, args):
     from buildman import test
     from buildman import test_boards
     from buildman import test_bsettings
+    from buildman import test_builder
 
     test_name = args.terms and args.terms[0] or None
     if skip_net_tests:
@@ -52,6 +53,7 @@  def run_tests(skip_net_tests, debug, verbose, args):
          test.TestBuildConfig, test.TestBuildMisc, test.TestBuilderFuncs,
          func_test.TestFunctional,
          test_boards.TestBoards, test_bsettings.TestBsettings,
+         test_builder.TestPrintFuncSizeDetail,
          'buildman.toolchain'])
 
     return (0 if result.wasSuccessful() else 1)
diff --git a/tools/buildman/test_builder.py b/tools/buildman/test_builder.py
new file mode 100644
index 00000000000..5d003de1966
--- /dev/null
+++ b/tools/buildman/test_builder.py
@@ -0,0 +1,144 @@ 
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright 2025 Google LLC
+# Written by Simon Glass <sjg@chromium.org>
+
+"""Unit tests for builder.py"""
+
+import unittest
+
+from buildman import builder
+from u_boot_pylib import terminal
+
+
+class TestPrintFuncSizeDetail(unittest.TestCase):
+    """Tests for Builder.print_func_size_detail()"""
+
+    def setUp(self):
+        """Set up test fixtures"""
+        # Create a minimal Builder for testing
+        self.builder = builder.Builder(
+            toolchains=None, base_dir='/tmp', git_dir=None, num_threads=0,
+            num_jobs=1)
+        terminal.set_print_test_mode()
+
+    def tearDown(self):
+        """Clean up after tests"""
+        terminal.set_print_test_mode(False)
+
+    def test_no_change(self):
+        """Test with no size changes"""
+        old = {'func_a': 100, 'func_b': 200}
+        new = {'func_a': 100, 'func_b': 200}
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        # No output when there are no changes
+        self.assertEqual(len(lines), 0)
+
+    def test_function_grows(self):
+        """Test when a function grows in size"""
+        old = {'func_a': 100}
+        new = {'func_a': 150}
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        text = '\n'.join(line.text for line in lines)
+        self.assertIn('u-boot', text)
+        self.assertIn('func_a', text)
+        self.assertIn('grow:', text)
+        # Check old, new and delta values appear
+        self.assertIn('100', text)
+        self.assertIn('150', text)
+        self.assertIn('+50', text)
+
+    def test_function_shrinks(self):
+        """Test when a function shrinks in size"""
+        old = {'func_a': 200}
+        new = {'func_a': 150}
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        text = '\n'.join(line.text for line in lines)
+        self.assertIn('func_a', text)
+        self.assertIn('-50', text)
+
+    def test_function_added(self):
+        """Test when a new function is added"""
+        old = {'func_a': 100}
+        new = {'func_a': 100, 'func_b': 200}
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        text = '\n'.join(line.text for line in lines)
+        self.assertIn('func_b', text)
+        self.assertIn('add:', text)
+        # New function shows '-' for old value
+        self.assertIn('-', text)
+        self.assertIn('200', text)
+
+    def test_function_removed(self):
+        """Test when a function is removed"""
+        old = {'func_a': 100, 'func_b': 200}
+        new = {'func_a': 100}
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        text = '\n'.join(line.text for line in lines)
+        self.assertIn('func_b', text)
+        # Removed function shows '-' for new value
+        self.assertIn('-200', text)
+
+    def test_mixed_changes(self):
+        """Test with a mix of added, removed, grown and shrunk functions"""
+        old = {
+            'unchanged': 100,
+            'grown': 200,
+            'shrunk': 300,
+            'removed': 400,
+        }
+        new = {
+            'unchanged': 100,
+            'grown': 250,
+            'shrunk': 250,
+            'added': 150,
+        }
+
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', old, new)
+        lines = terminal.get_print_test_lines()
+
+        text = '\n'.join(line.text for line in lines)
+        # Check all changed functions appear
+        self.assertIn('grown', text)
+        self.assertIn('shrunk', text)
+        self.assertIn('removed', text)
+        self.assertIn('added', text)
+        # unchanged should not appear (no delta)
+        # Check the header line appears
+        self.assertIn('function', text)
+        self.assertIn('old', text)
+        self.assertIn('new', text)
+        self.assertIn('delta', text)
+
+    def test_empty_dicts(self):
+        """Test with empty dictionaries"""
+        terminal.get_print_test_lines()  # Clear
+        self.builder.print_func_size_detail('u-boot', {}, {})
+        lines = terminal.get_print_test_lines()
+
+        # No output when both dicts are empty
+        self.assertEqual(len(lines), 0)
+
+
+if __name__ == '__main__':
+    unittest.main()