Adds tests for metrics filter and fixes key collision

When using multiple instances of the metrics filter,
the keys collided, making the counters interfere with
each other.

lib/logstash/filters/metrics.rb

@@ -1,3 +1,4 @@
+require "securerandom"
 require "logstash/filters/base"
 require "logstash/namespace"
 
@@ -132,6 +133,7 @@ class LogStash::Filters::Metrics < LogStash::Filters::Base
     require "socket"
     @last_flush = 0 # how many seconds ago the metrics where flushed.
     @last_clear = 0 # how many seconds ago the metrics where cleared.
+    @random_key_preffix = SecureRandom.hex
     initialize_metrics
   end # def register
 
@@ -211,8 +213,12 @@ class LogStash::Filters::Metrics < LogStash::Filters::Base
 
   private
   def initialize_metrics
-    @metric_meters = Hash.new { |h,k| h[k] = Metriks.meter(k) }
-    @metric_timers = Hash.new { |h,k| h[k] = Metriks.timer(k) }
+    @metric_meters = Hash.new { |h,k| h[k] = Metriks.meter metric_key(k) }
+    @metric_timers = Hash.new { |h,k| h[k] = Metriks.timer metric_key(k) }
+  end
+
+  def metric_key(key)
+    "#{@random_key_preffix}_#{key}"
   end
 
   def should_flush?

spec/filters/metrics.rb

@@ -0,0 +1,77 @@
+require "logstash/filters/metrics"
+
+describe LogStash::Filters::Metrics do
+
+  context "with basic config" do
+    context "when no events were received" do
+      it "should not flush" do
+        config = {"meter" => ["http.%{response}"]}
+        filter = LogStash::Filters::Metrics.new config
+        filter.register
+
+        events = filter.flush
+        insist { events }.nil?
+      end
+    end
+
+    context "when events are received" do
+      context "on the first flush" do
+        it "should flush counts" do
+          config = {"meter" => ["http.%{response}"]}
+          filter = LogStash::Filters::Metrics.new config
+          filter.register
+          filter.filter LogStash::Event.new({"response" => 200})
+          filter.filter LogStash::Event.new({"response" => 200})
+          filter.filter LogStash::Event.new({"response" => 404})
+
+          events = filter.flush
+          insist { events.length } == 1
+          insist { events.first["http.200.count"] } == 2
+          insist { events.first["http.404.count"] } == 1
+        end
+      end
+
+      context "on the second flush" do
+        it "should not reset counts" do
+          config = {"meter" => ["http.%{response}"]}
+          filter = LogStash::Filters::Metrics.new config
+          filter.register
+          filter.filter LogStash::Event.new({"response" => 200})
+          filter.filter LogStash::Event.new({"response" => 200})
+          filter.filter LogStash::Event.new({"response" => 404})
+
+          events = filter.flush
+          events = filter.flush
+          insist { events.length } == 1
+          insist { events.first["http.200.count"] } == 2
+          insist { events.first["http.404.count"] } == 1
+        end
+      end
+    end
+  end
+
+  context "with multiple instances" do
+    it "counts should be independent" do
+      config_tag1 = {"meter" => ["http.%{response}"], "tags" => ["tag1"]}
+      config_tag2 = {"meter" => ["http.%{response}"], "tags" => ["tag2"]}
+      filter_tag1 = LogStash::Filters::Metrics.new config_tag1
+      filter_tag2 = LogStash::Filters::Metrics.new config_tag2
+      event_tag1 = LogStash::Event.new({"response" => 200, "tags" => [ "tag1" ]})
+      event_tag2 = LogStash::Event.new({"response" => 200, "tags" => [ "tag2" ]})
+      event2_tag2 = LogStash::Event.new({"response" => 200, "tags" => [ "tag2" ]})
+      filter_tag1.register
+      filter_tag2.register
+
+      [event_tag1, event_tag2, event2_tag2].each do |event|
+        filter_tag1.filter event
+        filter_tag2.filter event
+      end
+
+      events_tag1 = filter_tag1.flush
+      events_tag2 = filter_tag2.flush
+
+      insist { events_tag1.first["http.200.count"] } == 1
+      insist { events_tag2.first["http.200.count"] } == 2
+    end
+  end
+end