diff --git a/aish/tests/test_strformat_utils.py b/aish/tests/test_strformat_utils.py
index 4c0e196..8671d47 100644
--- a/aish/tests/test_strformat_utils.py
+++ b/aish/tests/test_strformat_utils.py
@@ -17,5 +17,30 @@ def test_get_only_text_in_intervals():
 
 
 def test_get_only_text_in_intervals2():
-    result = get_highlighted_text("0123456789", ((0, 4), (7, 10)), excluded_exscape="-")
+    result = get_highlighted_text("0123456789", ((0, 4), (7, 10)), exclude_filler="-")
     assert result == "0123---789"
+
+
+def test_get_only_text_in_intervals_empty():
+    result = get_only_text_in_intervals("0123456789", (), exclude_filler="-")
+    assert result == "----------"
+
+
+def test_get_only_text_in_intervals_single():
+    result = get_only_text_in_intervals("0123456789", ((2, 5),), exclude_filler="*")
+    assert result == "**234*****"
+
+
+def test_get_highlighted_text_empty_intervals():
+    result = get_highlighted_text("0123456789", (), "S", "E", "!")
+    assert result == "E0123456789!"
+
+
+def test_get_highlighted_text_adjacent_intervals():
+    result = get_highlighted_text("0123456789", ((0, 3), (3, 6)), "S", "E", "!")
+    assert result == "S012ES345E6789!"
+
+
+def test_get_highlighted_text_single_char():
+    result = get_highlighted_text("abc", ((1, 2),), "[", "]", "")
+    assert result == "]a[b]c"