fix test formatting

src/ecdsa/test_der.py

diff --git a/src/ecdsa/test_der.py b/src/ecdsa/test_der.py
index 33a2dca..26909bc 100644
--- a/src/ecdsa/test_der.py
+++ b/src/ecdsa/test_der.py
@@ -601,22 +601,31 @@
     assert rest == b""
     assert decoded_oid == ids
 
+
 def test_remove_octet_string_rejects_truncated_length():
     # OCTET STRING: declared length 4096, but only 3 bytes present
     bad = b"\x04\x82\x10\x00" + b"ABC"
-    with pytest.raises(UnexpectedDER, match="Length longer than the provided buffer"):
+    with pytest.raises(
+        UnexpectedDER, match="Length longer than the provided buffer"
+    ):
         remove_octet_string(bad)
 
+
 def test_remove_constructed_rejects_truncated_length():
     # Constructed tag: 0xA0 (context-specific constructed, tag=0)
     # declared length 4096, but only 3 bytes present
     bad = b"\xA0\x82\x10\x00" + b"ABC"
-    with pytest.raises(UnexpectedDER, match="Length longer than the provided buffer"):
+    with pytest.raises(
+        UnexpectedDER, match="Length longer than the provided buffer"
+    ):
         remove_constructed(bad)
 
+
 def test_remove_implicit_rejects_truncated_length():
     # IMPLICIT primitive context-specific tag 0: 0x80
     # declared length 4096, but only 3 bytes present
     bad = b"\x80\x82\x10\x00" + b"ABC"
-    with pytest.raises(UnexpectedDER, match="Length longer than the provided buffer"):
+    with pytest.raises(
+        UnexpectedDER, match="Length longer than the provided buffer"
+    ):
         remove_implicit(bad)