Add a test to improve coverage in xmpsidecar.cpp

test/data/coverage_xmpsidecar_isXmpType.xmp

@@ -0,0 +1,3 @@
+<?xml                       <?xpacket
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+

tests/bugfixes/github/test_coverage_xmpsidecar_isXmpType.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+
+from system_tests import CaseMeta, path, check_no_ASAN_UBSAN_errors
+
+class coverage_xmpsidecar_isXmpType(metaclass=CaseMeta):
+    """
+    Test added to improve code coverage in xmpsidecar.cpp after
+    Codecov complained about a lack of code coverage in this PR:
+    https://github.com/Exiv2/exiv2/pull/1786
+    """
+
+    filename = path("$data_path/coverage_xmpsidecar_isXmpType.xmp")
+    commands = ["$exiv2 $filename"]
+    stderr = ["""Error: XMP Toolkit error 201: XML parsing failure
+Warning: Failed to decode XMP metadata.
+$filename: No Exif data found in the file
+"""]
+    retval = [253]
+
+    compare_stdout = check_no_ASAN_UBSAN_errors