Do not use trace on internal logger

The internal logger does not support `trace`. Use `debug` instead.

Since the heartbeat implementation intentionally swallows all errors
and logs them, issues such as this would go unnoticed by the test
suite. Add assertions on the messages that are expected to be
logged to ensure that the implementation is actually working as
expected.

.changesets/fix-issue-when-sending-heartbeats.md

@@ -0,0 +1,6 @@
+---
+bump: patch
+type: fix
+---
+
+Fix an issue where an error about the AppSignal internal logger is raised when sending a heartbeat.

lib/appsignal/heartbeat.rb

@@ -45,7 +45,7 @@ def transmit_event(kind)
       response = self.class.transmitter.transmit(event(kind))
 
       if response.code.to_i >= 200 && response.code.to_i < 300
-        Appsignal.internal_logger.trace("Transmitted heartbeat `#{name}` (#{id}) #{kind} event")
+        Appsignal.internal_logger.debug("Transmitted heartbeat `#{name}` (#{id}) #{kind} event")
       else
         Appsignal.internal_logger.error(
           "Failed to transmit heartbeat event: status code was #{response.code}"

spec/lib/appsignal/heartbeat_spec.rb

@@ -24,7 +24,26 @@
       expect(transmitter).to receive(:transmit).with(hash_including(
         :name => "heartbeat-name",
         :kind => "start"
-      )).and_return(nil)
+      )).and_return(Net::HTTPResponse.new(nil, "200", nil))
+
+      expect(Appsignal.internal_logger).to receive(:debug).with(
+        "Transmitted heartbeat `heartbeat-name` (#{heartbeat.id}) start event"
+      )
+      expect(Appsignal.internal_logger).not_to receive(:error)
+
+      heartbeat.start
+    end
+
+    it "should log an error if it fails" do
+      expect(transmitter).to receive(:transmit).with(hash_including(
+        :name => "heartbeat-name",
+        :kind => "start"
+      )).and_return(Net::HTTPResponse.new(nil, "499", nil))
+
+      expect(Appsignal.internal_logger).not_to receive(:debug)
+      expect(Appsignal.internal_logger).to receive(:error).with(
+        "Failed to transmit heartbeat event: status code was 499"
+      )
 
       heartbeat.start
     end
@@ -35,7 +54,26 @@
       expect(transmitter).to receive(:transmit).with(hash_including(
         :name => "heartbeat-name",
         :kind => "finish"
-      )).and_return(nil)
+      )).and_return(Net::HTTPResponse.new(nil, "200", nil))
+
+      expect(Appsignal.internal_logger).to receive(:debug).with(
+        "Transmitted heartbeat `heartbeat-name` (#{heartbeat.id}) finish event"
+      )
+      expect(Appsignal.internal_logger).not_to receive(:error)
+
+      heartbeat.finish
+    end
+
+    it "should log an error if it fails" do
+      expect(transmitter).to receive(:transmit).with(hash_including(
+        :name => "heartbeat-name",
+        :kind => "finish"
+      )).and_return(Net::HTTPResponse.new(nil, "499", nil))
+
+      expect(Appsignal.internal_logger).not_to receive(:debug)
+      expect(Appsignal.internal_logger).to receive(:error).with(
+        "Failed to transmit heartbeat event: status code was 499"
+      )
 
       heartbeat.finish
     end