core: Add test for negative observed histogram value

Fixes: #386
jupp0r · Nov 1, 2020 · 6d86e2d · 6d86e2d
1 parent efce85d
commit 6d86e2d
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Showing 2 changed files with 9 additions and 1 deletion.
diff --git a/core/include/prometheus/histogram.h b/core/include/prometheus/histogram.h
@@ -4,9 +4,9 @@
 
 #include "prometheus/client_metric.h"
 #include "prometheus/counter.h"
-#include "prometheus/gauge.h"
 #include "prometheus/detail/builder.h"
 #include "prometheus/detail/core_export.h"
+#include "prometheus/gauge.h"
 #include "prometheus/metric_type.h"
 
 namespace prometheus {

diff --git a/core/tests/histogram_test.cc b/core/tests/histogram_test.cc
@@ -108,5 +108,13 @@ TEST(HistogramTest, observe_multiple_test_length_error) {
   ASSERT_THROW(histogram.ObserveMultiple({5, 9}, 20), std::length_error);
 }
 
+TEST(HistogramTest, sum_can_go_down) {
+  Histogram histogram{{1}};
+  auto metric1 = histogram.Collect();
+  histogram.Observe(-10);
+  auto metric2 = histogram.Collect();
+  EXPECT_LT(metric2.histogram.sample_sum, metric1.histogram.sample_sum);
+}
+
 }  // namespace
 }  // namespace prometheus