test(metrics): unit test for incrementRequests

Author: gsantos-hc

agent-inject/metrics_test.go

@@ -4,6 +4,7 @@
 package agent_inject
 
 import (
+	"errors"
 	"testing"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -12,7 +13,8 @@ import (
 )
 
 func Test_incrementInjections(t *testing.T) {
-	MustRegisterInjectorMetrics(prometheus.DefaultRegisterer)
+	reg := prometheus.NewRegistry()
+	MustRegisterInjectorMetrics(reg)
 
 	tests := map[string]struct {
 		namespace      string
@@ -65,3 +67,33 @@ func Test_incrementInjections(t *testing.T) {
 		})
 	}
 }
+
+func Test_incrementRequests(t *testing.T) {
+	one := 1.0
+	reg := prometheus.NewRegistry()
+	MustRegisterInjectorMetrics(reg)
+
+	tests := map[string]struct {
+		err error
+	}{
+		"valid_request":        {err: nil},
+		"invalid_content_type": {err: errors.New("Invalid content-type: ")},
+		"error_reading_body":   {err: errors.New("error reading request body: ")},
+	}
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			// Unlike CounterVec, Counter does not have a Reset() method. As a workaround, we can
+			// collect the before and after counts and assert that the difference is 0 or 1, as
+			// applicable.
+			reqsExpected := testutil.ToFloat64(requestsReceived) + one
+			errsExpected := testutil.ToFloat64(requestsErrored)
+			if test.err != nil {
+				errsExpected += one
+			}
+
+			incrementRequests(test.err)
+			assert.Equal(t, reqsExpected, testutil.ToFloat64(requestsReceived))
+			assert.Equal(t, errsExpected, testutil.ToFloat64(requestsErrored))
+		})
+	}
+}