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diff --git a/batch.py b/batch.py
index 8846abe..9c1b0d9 100644
--- a/batch.py
+++ b/batch.py
@@ -11,11 +11,7 @@ def format_batch_as_table(batch, current_index=-1, max_rows=20):
         return "(Empty Batch)"
 
     # Get all unique keys across all rows
-    keys = []
-    for row in batch:
-        for k in row.keys():
-            if k not in keys:
-                keys.append(k)
+    keys = list(dict.fromkeys(itertools.chain.from_iterable(row.keys() for row in batch)))
 
     if not keys:
         return "(Empty rows)"
diff --git a/tests/test_batch.py b/tests/test_batch.py
new file mode 100644
index 0000000..0c3acd8
--- /dev/null
+++ b/tests/test_batch.py
@@ -0,0 +1,73 @@
+import unittest
+import sys
+import os
+import importlib.util
+from unittest.mock import MagicMock
+
+# --- Import setup (same as benchmark) ---
+mock_folder_paths = MagicMock()
+mock_folder_paths.folder_names_and_paths = {"checkpoint": ([], {})}
+sys.modules['folder_paths'] = mock_folder_paths
+sys.modules['torch'] = MagicMock()
+sys.modules['numpy'] = MagicMock()
+sys.modules['PIL'] = MagicMock()
+sys.modules['PIL.Image'] = MagicMock()
+sys.modules['PIL.ImageOps'] = MagicMock()
+sys.modules['PIL.ImageSequence'] = MagicMock()
+sys.modules['PIL.ImageFile'] = MagicMock()
+
+repo_root = os.getcwd()
+spec = importlib.util.spec_from_file_location("comfy_nodes", os.path.join(repo_root, "__init__.py"))
+comfy_nodes = importlib.util.module_from_spec(spec)
+sys.modules["comfy_nodes"] = comfy_nodes
+spec.loader.exec_module(comfy_nodes)
+
+format_batch_as_table = comfy_nodes.batch.format_batch_as_table
+
+class TestBatchFormat(unittest.TestCase):
+    def test_basic_batch(self):
+        batch = [{'a': 1, 'b': 2}, {'a': 3, 'b': 4}]
+        result = format_batch_as_table(batch)
+        self.assertIn("| a | b |", result)
+        self.assertIn("| 1 | 2 |", result)
+        self.assertIn("| 3 | 4 |", result)
+
+    def test_order_preservation(self):
+        # Keys should appear in order of first appearance
+        # Row 1 introduces 'b', 'a'
+        # Row 2 introduces 'c'
+        # Expected order: b, a, c
+        batch = [{'b': 1, 'a': 2}, {'c': 3}]
+        result = format_batch_as_table(batch)
+        # Check header line
+        lines = result.split('\n')
+        header = lines[0]
+        # We expect something like "| b | a | c |"
+        # Spacing might vary depending on value lengths, so we check order in string
+        self.assertTrue(header.index('b') < header.index('a'))
+        self.assertTrue(header.index('a') < header.index('c'))
+
+    def test_disjoint_keys(self):
+        batch = [{'a': 1}, {'b': 2}]
+        result = format_batch_as_table(batch)
+        self.assertIn("| a | b |", result)
+        # Row 1 should have empty for b
+        # Row 2 should have empty for a
+        # Note: Current implementation puts empty string for missing keys
+
+        # Verify row 1 has '1' and empty for 'b'
+        # Since we don't know exact spacing easily, we trust the table formatter logic
+        # but ensure no crash and content is there.
+        self.assertIn("1", result)
+        self.assertIn("2", result)
+
+    def test_empty_batch(self):
+        result = format_batch_as_table([])
+        self.assertEqual(result, "(Empty Batch)")
+
+    def test_empty_rows(self):
+        result = format_batch_as_table([{}, {}])
+        self.assertEqual(result, "(Empty rows)")
+
+if __name__ == '__main__':
+    unittest.main()