diff --git a/tests/test_util.py b/tests/test_util.py
new file mode 100644
index 00000000..73f7c5b1
--- /dev/null
+++ b/tests/test_util.py
@@ -0,0 +1,25 @@
+from gptme.tools import is_supported_codeblock
+
+
+def test_is_supported_codeblock():
+    block_plain = """```
+some plaintext
+```
+"""
+    # clean unsupported block
+    assert not is_supported_codeblock(block_plain)
+
+    block_python = """```python
+print("hello world")
+```
+"""
+    # clean supported block
+    assert is_supported_codeblock(block_python)
+
+    # has preamble
+    s = f"""bla bla\n{block_python}"""
+    assert is_supported_codeblock(s)
+
+    # last block is plain/unsupported
+    s = f"""bla bla\n{block_python}\nbla bla{block_plain}"""
+    assert not is_supported_codeblock(s)