Fix handling of empty and missing tag values with standard formatter

lib/telemetry_metrics_statsd/formatter/standard.ex

@@ -58,11 +58,11 @@ defmodule TelemetryMetricsStatsd.Formatter.Standard do
   end
 
   defp do_format_metric_tags([{_, nil} | tags]) do
-    [?., "nil" | format_metric_tags(tags)]
+    [?., "nil" | do_format_metric_tags(tags)]
   end
 
   defp do_format_metric_tags([{_, tag_value} | tags]) do
-    [?., to_string(tag_value) | format_metric_tags(tags)]
+    [?., to_string(tag_value) | do_format_metric_tags(tags)]
   end
 
   defp format_metric_value(%Metrics.Counter{}, _value), do: "1|c"

test/telemetry_metrics_statsd/formatter/standard_test.exs

@@ -64,14 +64,14 @@ defmodule TelemetryMetricsStatsd.Formatter.StandardTest do
   test "nil tags are included in the formatted metric" do
     m = given_last_value("my.awesome.metric", tags: [:method, :status])
 
-    assert format(m, 131, method: nil, status: 200) ==
-             "my.awesome.metric.nil.200:131|g"
+    assert format(m, 131, method: "GET", status: nil) ==
+             "my.awesome.metric.GET.nil:131|g"
   end
 
   test "empty string tag values are dropped" do
     m = given_last_value("my.awesome.metric", tags: [:method, :status])
 
-    assert format(m, 131, method: "", status: 200) == ""
+    assert format(m, 131, method: "GET", status: "") == ""
   end
 
   test "tags passed as explicit argument are used for the formatted metric" do

test/telemetry_metrics_statsd_test.exs

@@ -144,7 +144,45 @@ defmodule TelemetryMetricsStatsdTest do
              "invalid value for :formatter option: expected :formatter be either :standard or :datadog, got :my_formatter"
   end
 
-  test "it doesn't crash when tag values are missing" do
+  test "it doesn't crash when tag values are missing with standard formatter" do
+    {socket, port} = given_udp_port_opened()
+
+    counter = given_counter("http.request.count", tags: [:method, :status])
+
+    start_reporter(
+      metrics: [counter],
+      port: port
+    )
+
+    handlers_before = :telemetry.list_handlers([])
+
+    :telemetry.execute([:http, :request], %{latency: 172}, %{method: "GET"})
+    assert_reported(socket, "")
+
+    handlers_after = :telemetry.list_handlers([])
+    assert handlers_after == handlers_before
+  end
+
+  test "it doesn't crash when tag values are nil with standard formatter" do
+    {socket, port} = given_udp_port_opened()
+
+    counter = given_counter("http.request.count", tags: [:method, :status])
+
+    start_reporter(
+      metrics: [counter],
+      port: port
+    )
+
+    handlers_before = :telemetry.list_handlers([])
+
+    :telemetry.execute([:http, :request], %{latency: 172}, %{method: "GET", status: nil})
+    assert_reported(socket, "http.request.count.GET.nil:1|c")
+
+    handlers_after = :telemetry.list_handlers([])
+    assert handlers_after == handlers_before
+  end
+
+  test "it doesn't crash when tag values are missing with DataDog formatter" do
     {socket, port} = given_udp_port_opened()
 
     counter = given_counter("http.request.count", tags: [:method, :status])