Flags to configure eventing upgrade tests forwarder (ksvc) (#3899)

* Flags to configure eventing upgrade tests forwarder (ksvc)

This change is required to complete knative/operator#252

It enables configuring of wathola forwarder implemented as Knative
Service. Configuration is done by using new optional environment
variables.

* Using kelseyhightower/envconfig after code review

* Docs for Eventing upgrade tests config overrides.

test/upgrade/README.md

@@ -83,3 +83,23 @@ Diagram below describe the setup:
           +--------+       +---------+ |
            (default)        +----------+
 ```
+
+#### Probe test configuration
+
+Probe test behavior can be influenced from outside without modifying its source
+code. That can be beneficial if one would like to run upgrade tests in different
+context. One such example might be running Eventing upgrade tests in place that
+have Serving and Eventing both installed. In such environment one can set
+environment variable `E2E_UPGRADE_TESTS_SERVING_USE` to enable usage of ksvc
+forwarder (which is disabled by default):
+
+```
+$ export E2E_UPGRADE_TESTS_SERVING_USE=true
+```
+
+Any option, apart from namespace, in
+[`knative.dev/eventing/test/upgrade/prober.Config`](https://github.com/knative/eventing/blob/022e281/test/upgrade/prober/prober.go#L52-L63)
+struct can be influenced, by using `E2E_UPGRADE_TESTS_XXXXX` environmental
+variable prefix (using
+[kelseyhightower/envconfig](https://github.com/kelseyhightower/envconfig#usage)
+usage).

test/upgrade/prober/prober.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/kelseyhightower/envconfig"
 	"github.com/wavesoftware/go-ensure"
 	"go.uber.org/zap"
 	testlib "knative.dev/eventing/test/lib"
@@ -63,8 +64,8 @@ type ServingConfig struct {
 }
 
 func NewConfig(namespace string) *Config {
-	return &Config{
-		Namespace:     namespace,
+	config := &Config{
+		Namespace:     "",
 		Interval:      Interval,
 		FinishedSleep: 5 * time.Second,
 		FailOnErrors:  true,
@@ -73,6 +74,10 @@ func NewConfig(namespace string) *Config {
 			ScaleToZero: true,
 		},
 	}
+	err := envconfig.Process("e2e_upgrade_tests", config)
+	ensure.NoError(err)
+	config.Namespace = namespace
+	return config
 }
 
 // RunEventProber starts a single Prober of the given domain.
@@ -151,7 +156,7 @@ func (p *prober) remove() {
 	if p.config.Serving.Use {
 		p.removeForwarder()
 	}
-	p.client.Tracker.Clean(true)
+	ensure.NoError(p.client.Tracker.Clean(true))
 }
 
 func newProber(log *zap.SugaredLogger, client *testlib.Client, config *Config) Prober {

test/upgrade/prober/prober_test.go

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2020 The Knative 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.
+ */
+
+package prober
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type envValue uint
+
+const (
+	EnvFalse envValue = iota
+	EnvTrue
+	EnvUnset
+)
+
+func TestNewConfig(t *testing.T) {
+	envname := "E2E_UPGRADE_TESTS_SERVING_USE"
+	suite := []struct {
+		env envValue
+		out bool
+	}{
+		{EnvFalse, false},
+		{EnvTrue, true},
+		{EnvUnset, false},
+	}
+	for _, s := range suite {
+		t.Run(fmt.Sprintf("env=%v,out=%t", s.env, s.out), func(t *testing.T) {
+			if s.env != EnvUnset {
+				val := "false"
+				if s.env == EnvTrue {
+					val = "true"
+				}
+				assert.NoError(t, os.Setenv(envname, val))
+				defer func() { assert.NoError(t, os.Unsetenv(envname)) }()
+			}
+			config := NewConfig("test-ns")
+
+			assert.Equal(t, s.out, config.Serving.Use)
+			assert.True(t, config.Serving.ScaleToZero)
+		})
+	}
+}