Adding tests for the heap calculation, also changed the visibility

In retrospect, it just easier to expose the methods in the jvm spec
monitoring to be able to test them in isolation.

Fixes #6827

logstash-core/lib/logstash/instrument/periodic_poller/jvm.rb

@@ -34,6 +34,13 @@ module LogStash module Instrument module PeriodicPoller
       end
     end
 
+    MEMORY_TRANSPOSE_MAP = {
+      "usage.used" => :used_in_bytes,
+      "usage.committed" => :committed_in_bytes,
+      "usage.max" => :max_in_bytes,
+      "peak.max" => :peak_max_in_bytes,
+      "peak.used" => :peak_used_in_bytes
+    }
 
     attr_reader :metric
 
@@ -52,8 +59,6 @@ module LogStash module Instrument module PeriodicPoller
       collect_load_average
     end
 
-    private
-
     def collect_gc_stats
       garbage_collectors = ManagementFactory.getGarbageCollectorMXBeans()
 
@@ -141,7 +146,6 @@ module LogStash module Instrument module PeriodicPoller
       end
     end
 
-
     def build_pools_metrics(data)
       heap = data["heap"]
       old  = {}
@@ -161,19 +165,11 @@ module LogStash module Instrument module PeriodicPoller
     end
 
     def aggregate_information_for(collection)
-      transpose_map = {
-        "usage.used" => :used_in_bytes,
-        "usage.committed" => :committed_in_bytes,
-        "usage.max" => :max_in_bytes,
-        "peak.max" => :peak_max_in_bytes,
-        "peak.used" => :peak_used_in_bytes
-
-      }
       collection.reduce(default_information_accumulator) do |m,e|
         e = { e[0] => e[1] } if e.is_a?(Array)
         e.each_pair do |k,v|
-          if transpose_map.include?(k)
-            transpose_key = transpose_map[k]
+          if MEMORY_TRANSPOSE_MAP.include?(k)
+            transpose_key = MEMORY_TRANSPOSE_MAP[k]
             m[transpose_key] += v
           end
         end

logstash-core/spec/logstash/instrument/periodic_poller/jvm_spec.rb

@@ -54,6 +54,41 @@ describe LogStash::Instrument::PeriodicPoller::JVM do
     end
   end
 
+  describe "aggregate heap information" do
+    shared_examples "heap_information" do
+      let(:data_set) do
+        {
+          "usage.used" => 5,
+          "usage.committed" => 11,
+          "usage.max" => 21,
+          "peak.max" => 51,
+          "peak.used" => 61
+        }
+      end
+      let(:collection) { [data_set] }
+
+      it "return the right values" do
+        expect(subject.aggregate_information_for(collection)).to match({
+          :used_in_bytes => 5 * collection.size,
+          :committed_in_bytes => 11 * collection.size,
+          :max_in_bytes => 21 * collection.size,
+          :peak_max_in_bytes => 51 * collection.size,
+          :peak_used_in_bytes => 61 * collection.size
+        })
+      end
+    end
+
+    context "with only one data set in a collection" do
+      include_examples "heap_information"
+    end
+
+    context "with multiples data set in a collection" do
+      include_examples "heap_information" do
+        let(:collection) { ar = []; ar << data_set; ar << data_set; ar }
+      end
+    end
+  end
+
   describe "collections" do
     subject(:collection) { jvm.collect }
     it "should run cleanly" do