Add more helpers to pipeline/testing package (#19405)

(cherry picked from commit fac91b3)

libbeat/publisher/testing/connector.go

@@ -17,43 +17,118 @@
 
 package testing
 
-import "github.com/elastic/beats/v7/libbeat/beat"
+import (
+	"github.com/elastic/beats/v7/libbeat/beat"
+	"github.com/elastic/beats/v7/libbeat/common/atomic"
+)
 
+// ClientCounter can be used to create a beat.PipelineConnector that count
+// pipeline connects and disconnects.
+type ClientCounter struct {
+	total  atomic.Int
+	active atomic.Int
+}
+
+// FakeConnector implements the beat.PipelineConnector interface.
+// The ConnectFunc is called for each connection attempt, and must be provided
+// by tests that wish to use FakeConnector. If ConnectFunc is nil tests will panic
+// if there is a connection attempt.
 type FakeConnector struct {
 	ConnectFunc func(beat.ClientConfig) (beat.Client, error)
 }
 
+// FakeClient implements the beat.Client interface. The implementation of a
+// custom PublishFunc and CloseFunc are optional.
 type FakeClient struct {
+	// If set PublishFunc is called for each event that is published by a producer.
 	PublishFunc func(beat.Event)
-	CloseFunc   func() error
+
+	// If set CloseFunc is called on Close. Otherwise Close returns nil.
+	CloseFunc func() error
 }
 
 var _ beat.PipelineConnector = FakeConnector{}
 var _ beat.Client = (*FakeClient)(nil)
 
+// ConnectWith calls the ConnectFunc with the given configuration.
 func (c FakeConnector) ConnectWith(cfg beat.ClientConfig) (beat.Client, error) {
 	return c.ConnectFunc(cfg)
 }
 
+// Connect calls the ConnectFunc with an empty configuration.
 func (c FakeConnector) Connect() (beat.Client, error) {
 	return c.ConnectWith(beat.ClientConfig{})
 }
 
+// Publish calls PublishFunc, if PublishFunc is not nil.
 func (c *FakeClient) Publish(event beat.Event) {
 	if c.PublishFunc != nil {
 		c.PublishFunc(event)
 	}
 }
 
+// Close calls CloseFunc, if CloseFunc is not nil. Otherwise it returns nil.
 func (c *FakeClient) Close() error {
 	if c.CloseFunc == nil {
 		return nil
 	}
 	return c.CloseFunc()
 }
 
+// PublishAll calls PublishFunc for each event in the given slice.
 func (c *FakeClient) PublishAll(events []beat.Event) {
 	for _, event := range events {
 		c.Publish(event)
 	}
 }
+
+// FailingConnector creates a pipeline that will always fail with the
+// configured error value.
+func FailingConnector(err error) beat.PipelineConnector {
+	return &FakeConnector{
+		ConnectFunc: func(_ beat.ClientConfig) (beat.Client, error) {
+			return nil, err
+		},
+	}
+}
+
+// ConstClient returns a pipeline that always returns the pre-configured beat.Client instance.
+func ConstClient(client beat.Client) beat.PipelineConnector {
+	return &FakeConnector{
+		ConnectFunc: func(_ beat.ClientConfig) (beat.Client, error) {
+			return client, nil
+		},
+	}
+}
+
+// ChClient create a beat.Client that will forward all events to the given channel.
+func ChClient(ch chan beat.Event) beat.Client {
+	return &FakeClient{
+		PublishFunc: func(event beat.Event) {
+			ch <- event
+		},
+	}
+}
+
+// Active returns the number of currently active connections.
+func (c *ClientCounter) Active() int { return c.active.Load() }
+
+// Total returns the total number of calls to Connect.
+func (c *ClientCounter) Total() int { return c.total.Load() }
+
+// BuildConnector create a pipeline that updates the active and tocal
+// connection counters on Connect and Close calls.
+func (c *ClientCounter) BuildConnector() beat.PipelineConnector {
+	return FakeConnector{
+		ConnectFunc: func(_ beat.ClientConfig) (beat.Client, error) {
+			c.total.Inc()
+			c.active.Inc()
+			return &FakeClient{
+				CloseFunc: func() error {
+					c.active.Dec()
+					return nil
+				},
+			}, nil
+		},
+	}
+}