Add tags and namespace options to listen_for_error (#357)

`Appsignal.listen_for_error` is the only helper that doesn't support
custom tags and a custom namespace.
This change adds support for the tags and namespace and passes the
values along to `Appsignal.send_error`.

Did not change this spec to use `Appsignal::Transaction#to_h`, because
the change would be a lot more involved as we can't fetch the current
transaction from the current thread. To record a transaction we'd need
to be able to capture the transaction as it's being created.

lib/appsignal.rb

@@ -217,10 +217,37 @@ def monitor_single_transaction(name, env = {}, &block)
       stop("monitor_single_transaction")
     end
 
-    def listen_for_error
+    # Listen for an error to occur and send it to AppSignal.
+    #
+    # Uses {.send_error} to directly send the error in a separate transaction.
+    # Does not add the error to the current transaction.
+    #
+    # Make sure that AppSignal is integrated in your application beforehand.
+    # AppSignal won't record errors unless {Config#active?} is `true`.
+    #
+    # @example
+    #   # my_app.rb
+    #   # setup AppSignal beforehand
+    #
+    #   Appsignal.listen_for_error do
+    #     # my code
+    #     raise "foo"
+    #   end
+    #
+    # @see Transaction.set_tags
+    # @see Transaction.set_namespace
+    # @see .send_error
+    # @see https://docs.appsignal.com/ruby/instrumentation/integrating-appsignal.html
+    #   AppSignal integration guide
+    #
+    # @param tags [Hash, nil]
+    # @param namespace [String] the namespace for this error.
+    # @yield yields the given block.
+    # @return [Object] returns the return value of the given block.
+    def listen_for_error(tags = nil, namespace = Appsignal::Transaction::HTTP_REQUEST)
       yield
     rescue Exception => error # rubocop:disable Lint/RescueException
-      send_error(error)
+      send_error(error, tags, namespace)
       raise error
     end
     alias :listen_for_exception :listen_for_error

spec/lib/appsignal_spec.rb

@@ -257,7 +257,7 @@
     end
 
     describe ".listen_for_error" do
-      it "should do nothing" do
+      it "does not record anyhing" do
         error = RuntimeError.new("specific error")
         expect do
           Appsignal.listen_for_error do
@@ -779,13 +779,47 @@
     end
 
     describe ".listen_for_error" do
-      it "should call send_error and re-raise" do
-        expect(Appsignal).to receive(:send_error).with(kind_of(Exception))
+      it "records the error and re-raise it" do
+        expect(Appsignal).to receive(:send_error).with(
+          kind_of(ExampleException),
+          nil,
+          Appsignal::Transaction::HTTP_REQUEST
+        )
         expect do
           Appsignal.listen_for_error do
-            raise "I am an exception"
+            raise ExampleException, "I am an exception"
           end
-        end.to raise_error(RuntimeError, "I am an exception")
+        end.to raise_error(ExampleException, "I am an exception")
+      end
+
+      context "with tags" do
+        it "adds tags to the transaction" do
+          expect(Appsignal).to receive(:send_error).with(
+            kind_of(ExampleException),
+            { "foo" => "bar" },
+            Appsignal::Transaction::HTTP_REQUEST
+          )
+          expect do
+            Appsignal.listen_for_error("foo" => "bar") do
+              raise ExampleException, "I am an exception"
+            end
+          end.to raise_error(ExampleException, "I am an exception")
+        end
+      end
+
+      context "with a custom namespace" do
+        it "adds the namespace to the transaction" do
+          expect(Appsignal).to receive(:send_error).with(
+            kind_of(ExampleException),
+            nil,
+            "custom_namespace"
+          )
+          expect do
+            Appsignal.listen_for_error(nil, "custom_namespace") do
+              raise ExampleException, "I am an exception"
+            end
+          end.to raise_error(ExampleException, "I am an exception")
+        end
       end
     end