improve coverage

tests/test_filters.py

@@ -6,19 +6,21 @@
 from io import BytesIO
 from itertools import product as cartesian_product
 from pathlib import Path
+from unittest import mock
 
 import pytest
 from PIL import Image
 
 from pypdf import PdfReader
-from pypdf.errors import DeprecationError, PdfReadError
+from pypdf.errors import DependencyError, DeprecationError, PdfReadError
 from pypdf.filters import (
     ASCII85Decode,
     ASCIIHexDecode,
     CCITParameters,
     CCITTFaxDecode,
     CCITTParameters,
     FlateDecode,
+    JBIG2Decode,
 )
 from pypdf.generic import ArrayObject, DictionaryObject, IndirectObject, NameObject, NumberObject
 
@@ -642,3 +644,25 @@ def test_ascii85decode__non_recoverable(caplog):
     with pytest.raises(ValueError, match="Non-Ascii85 digit found: Ã"):
         ASCII85Decode.decode(data)
     assert caplog.text == ""
+
+
+def test_jbig2decode__binary_errors():
+    with (
+            mock.patch("pypdf.filters._JBIG2DEC_BINARY", None),
+            pytest.raises(DependencyError, match="jbig2dec binary is not available.")
+    ):
+        JBIG2Decode.decode(b"dummy")
+
+    result = subprocess.CompletedProcess(
+        args=["dummy"], returncode=0, stdout=b"",
+        stderr=(
+            b"jbig2dec: unrecognized option '--embedded'\n"
+            b"Usage: jbig2dec [options] <file.jbig2>\n"
+            b"   or  jbig2dec [options] <global_stream> <page_stream>\n"
+        )
+    )
+    with (
+            mock.patch("pypdf.filters.subprocess.run", return_value=result),
+            pytest.raises(DependencyError, match="jbig2dec>=0.15 is required.")
+    ):
+        JBIG2Decode.decode(b"dummy")