perf test: Test 2 libpfm4 error cases

Proposed in:

https://lore.kernel.org/lkml/20210517140931.2559364-1-tmricht@linux.ibm.com/Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20210519151213.2643570-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/pfm.c

@@ -155,6 +155,16 @@ static int test__pfm_group(void)
 			.nr_events = 3,
 			.nr_groups = 1,
 		},
+		{
+			.events = "instructions}",
+			.nr_events = 1,
+			.nr_groups = 0,
+		},
+		{
+			.events = "{{instructions}}",
+			.nr_events = 0,
+			.nr_groups = 0,
+		},
 	};
 
 	for (i = 0; i < ARRAY_SIZE(table); i++) {