added support for onChange report

Report is now notified when metric changes and updates reading values.

Tested:
  - Added new unit tests
  - OnChange report updates Readings when metric values changes

Change-Id: I3be9ef7aa0486cb15bac627aa1de5cc632613b3b
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/tests/src/test_report_manager.cpp b/tests/src/test_report_manager.cpp
index f4ce184..55b5a3c 100644
--- a/tests/src/test_report_manager.cpp
+++ b/tests/src/test_report_manager.cpp
@@ -121,6 +121,19 @@
     EXPECT_THAT(path, Eq(reportMock.getPath()));
 }
 
+TEST_F(TestReportManager, addOnChangeReport)
+{
+    EXPECT_CALL(reportFactoryMock, convertMetricParams(_, _));
+    reportFactoryMock
+        .expectMake(reportParams.reportingType(ReportingType::onChange),
+                    Ref(*sut), Ref(storageMock))
+        .WillOnce(Return(ByMove(std::move(reportMockPtr))));
+
+    auto [ec, path] = addReport(reportParams);
+    EXPECT_THAT(ec.value(), Eq(boost::system::errc::success));
+    EXPECT_THAT(path, Eq(reportMock.getPath()));
+}
+
 TEST_F(TestReportManager, nameIsUsedToGenerateIdWhenIdIsEmptyInAddReport)
 {
     reportParams.reportId("ReportName");