qapi: Add test for nonexistent schema file

This tests the error-return pathway introduced in the previous commit.
(Thanks to Paolo for the help with the Meson magic.)

Signed-off-by: John Snow <jsnow@redhat.com>

Message-Id: <20210519183951.3946870-3-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

tests/qapi-schema/meson.build

@@ -199,11 +199,16 @@ schemas = [
   'unknown-escape.json',
   'unknown-expr-key.json',
 ]
+schemas = files(schemas)
+
+# Intentionally missing schema file test -- not passed through files():
+schemas += [meson.current_source_dir() / 'missing-schema.json']
 
 # Because people may want to use test-qapi.py from the command line, we
 # are not using the "#! /usr/bin/env python3" trick here.  See
 # docs/devel/build-system.txt
-test('QAPI schema regression tests', python, args: files('test-qapi.py', schemas),
+test('QAPI schema regression tests', python,
+     args: files('test-qapi.py') + schemas,
      env: test_env, suite: ['qapi-schema', 'qapi-frontend'])
 
 diff = find_program('diff')

tests/qapi-schema/missing-schema.err

@@ -0,0 +1 @@
+can't read schema file 'missing-schema.json': No such file or directory