Preemprively raise an error on wrong level

Author: rhpvorderman

src/isal/igzip_threaded.py

@@ -172,6 +172,10 @@ def __init__(self,
                  level: int = isal_zlib.ISAL_DEFAULT_COMPRESSION,
                  threads: int = 1,
                  queue_size: int = 2):
+        if level < 0 or level > 3:
+            raise ValueError(
+                f"Invalid compression level, "
+                f"level should be between 0 and 3: {level}")
         self.lock = threading.Lock()
         self.exception: Optional[Exception] = None
         self.raw = fp

tests/test_igzip_threaded.py

@@ -73,9 +73,11 @@ def test_threaded_read_error():
 
 
 @pytest.mark.timeout(5)
-def test_threaded_write_error():
+def test_threaded_write_error(monkeypatch):
     tmp = tempfile.mktemp()
-    with pytest.raises(ValueError) as error:
-        with igzip_threaded.open(tmp, "wb", compresslevel=43) as writer:
+    # Compressobj method is called in a worker thread.
+    monkeypatch.delattr(igzip_threaded.isal_zlib, "compressobj")
+    with pytest.raises(AttributeError) as error:
+        with igzip_threaded.open(tmp, "wb", compresslevel=3) as writer:
             writer.write(b"x")
-    error.match("compression level")
+    error.match("no attribute 'compressobj'")