test: replace the SVG validity test with a pytest-based one

This python test splits out the various checks into individual tests and
python's assertions allow for messages. This should make debugging SVG
failures a lot easier.

One extra check over the C version of the test: we now check that we
only have one element for any given ID.

meson.build

@@ -235,7 +235,6 @@ endif
 ############# tests ############################
 
 if get_option('tests').enabled()
-	dep_libxml  = dependency('libxml-2.0', required : false)
 	dep_dl      = cc.find_library('dl')
 
 	tests_cflags = ['-DTOPSRCDIR="@0@"'.format(meson.current_source_dir())]
@@ -272,16 +271,6 @@ if get_option('tests').enabled()
 					 install: false)
 	test('test-stylus-validity', test_stylus_validity, suite: ['all', 'valgrind'])
 
-	if dep_libxml.found()
-		test_svg_validity = executable('test-svg-validity',
-					       'test/test-tablet-svg-validity.c',
-					       dependencies: [dep_libwacom, dep_libxml, dep_glib],
-					       include_directories: [includes_src],
-					       c_args: tests_cflags,
-					       install: false)
-		test('test-svg-validity', test_svg_validity, suite: ['all', 'valgrind'])
-	endif
-
 	valgrind = find_program('valgrind', required : false)
 	if valgrind.found()
 		valgrind_suppressions_file = dir_test / 'valgrind.suppressions'