libcamera: yaml-parser: Add failing test for unexpected behavior

When accessing a nonexistent key on a dict the YamlObject returns an
empty element. This element can happily be cast to a string. This is
unexpected. For example the following statement:

yamlDict["nonexistent"].get<string>("default")

is expected to return "default" but actually returns "". Add a (failing)
testcase for that behavior.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

test/yaml-parser.cpp

@@ -536,6 +536,12 @@ protected:
 			return TestFail;
 		}
 
+		/* Test access to nonexistent member. */
+		if (dictObj["nonexistent"].get<std::string>("default") != "default") {
+			cerr << "Accessing nonexistent dict entry fails to return default" << std::endl;
+			return TestFail;
+		}
+
 		/* Make sure utils::map_keys() works on the adapter. */
 		(void)utils::map_keys(dictObj.asDict());