Improve TarIO test coverage

Tests/test_file_tar.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import warnings
+from pathlib import Path
 
 import pytest
 
@@ -29,6 +30,22 @@
                 assert im.format == format
 
 
+def test_unexpected_end(tmp_path: Path) -> None:
+    tmpfile = str(tmp_path / "temp.tar")
+    with open(tmpfile, "w"):
+        pass
+
+    with pytest.raises(OSError, match="unexpected end of tar file"):
+        with TarIO.TarIO(tmpfile, "test"):
+            pass
+
+
+def test_cannot_find_subfile() -> None:
+    with pytest.raises(OSError, match="cannot find subfile"):
+        with TarIO.TarIO(TEST_TAR_FILE, "test"):
+            pass
+
+
 @pytest.mark.skipif(is_pypy(), reason="Requires CPython")
 def test_unclosed_file() -> None:
     with pytest.warns(ResourceWarning):