Add metrics implementation* Covers proxy service on server side* Update documentation

internal/metrics/exporter_test.go

@@ -0,0 +1,27 @@
+package metrics
+
+import (
+	"bytes"
+	"io/ioutil"
+	"net/http/httptest"
+	"regexp"
+	"testing"
+)
+
+func Test_newPromHTTPHandler(t *testing.T) {
+	h := newPromHTTPHandler()
+
+	req := httptest.NewRequest("GET", "http://test.local/metrics", new(bytes.Buffer))
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	resp := rec.Result()
+	b, _ := ioutil.ReadAll(resp.Body)
+
+	if resp == nil || resp.StatusCode != 200 {
+		t.Errorf("Metrics endpoint failed to respond: %s", b)
+	}
+
+	if m, _ := regexp.Match("^# HELP .*", b); !m {
+		t.Errorf("Metrics endpoint did not contain any help messages: %s", b)
+	}
+}