e2e: Invoke monitoring tests from single location

This commit adds a test function which initialises the prometheus client
and then passes it to the prometheus tests that need it.

This approach is preferable over creating a new port-forward for every
test is because initialising a port forward takes around 3-4 seconds and
this can significantly increase the total running time of tests. Reusing
port forward connection and prometheus client saves time for test.

And having a single place of creating port forward and client
intialisation ensures that we close that connection gracefully.

Signed-off-by: Suraj Deshmukh <suraj@kinvolk.io>

test/monitoring/monitoring_test.go

@@ -0,0 +1,70 @@
+// Copyright 2020 The Lokomotive Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build aws packet
+// +build poste2e
+
+package monitoring
+
+import (
+	"fmt"
+	"testing"
+
+	testutil "github.com/kinvolk/lokomotive/test/components/util"
+
+	"github.com/prometheus/client_golang/api"
+	v1 "github.com/prometheus/client_golang/api/prometheus/v1"
+)
+
+func TestPrometheus(t *testing.T) {
+	const prometheusPodPort = 9090
+
+	p := &testutil.PortForwardInfo{
+		PodName:   "prometheus-prometheus-operator-prometheus-0",
+		Namespace: "monitoring",
+		PodPort:   prometheusPodPort,
+	}
+
+	p.PortForward(t)
+	defer p.CloseChan()
+	p.WaitUntilForwardingAvailable(t)
+
+	promClient, err := api.NewClient(api.Config{
+		Address: fmt.Sprintf("http://127.0.0.1:%d", p.LocalPort),
+	})
+	if err != nil {
+		t.Fatalf("Error creating client: %v", err)
+	}
+
+	v1api := v1.NewAPI(promClient)
+
+	// Add to the list all the prometheus tests that should be invoked one at a time
+	tests := []struct {
+		Name string
+		Func func(*testing.T, v1.API)
+	}{
+		{
+			Name: "ControlPlaneMetrics",
+			Func: testControlPlanePrometheusMetrics,
+		},
+	}
+
+	// Invoke the test functions passing them the test object and the prometheus client.
+	for _, test := range tests {
+		test := test
+		t.Run(test.Name, func(t *testing.T) {
+			test.Func(t, v1api)
+		})
+	}
+}