Created metric class

Metric collects updates from sensor. Report displays metric readings
depending on reportingType.

Tested:
  - Added new units tests for Metric class
  - All other unit tests are passing

Change-Id: I19f4831fab163a4f9540cef7bb23e903ae90fddf
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/tests/src/helpers/metric_value_helpers.hpp b/tests/src/helpers/metric_value_helpers.hpp
new file mode 100644
index 0000000..f21d42a
--- /dev/null
+++ b/tests/src/helpers/metric_value_helpers.hpp
@@ -0,0 +1,17 @@
+#pragma once
+
+#include "metric_value.hpp"
+
+#include <gmock/gmock.h>
+
+inline void PrintTo(const MetricValue& o, std::ostream* os)
+{
+    (*os) << "{ id: " << o.id << ", metadata: " << o.metadata
+          << ", value: " << o.value << ", timestamp: " << o.timestamp << " }";
+}
+
+inline bool operator==(const MetricValue& left, const MetricValue& right)
+{
+    return std::tie(left.id, left.metadata, left.value, left.timestamp) ==
+           std::tie(right.id, right.metadata, right.value, right.timestamp);
+}
\ No newline at end of file