diff --git a/source-google-pubsub/emitter_test.go b/source-google-pubsub/emitter_test.go
new file mode 100644
index 0000000000..39da3f0887
--- /dev/null
+++ b/source-google-pubsub/emitter_test.go
@@ -0,0 +1,168 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"strconv"
+	"sync"
+	"testing"
+
+	"cloud.google.com/go/pubsub"
+	boilerplate "github.com/estuary/connectors/source-boilerplate"
+	pc "github.com/estuary/flow/go/protocols/capture"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sync/errgroup"
+	"google.golang.org/grpc/metadata"
+)
+
+func TestEmitter(t *testing.T) {
+	testSrv := &TestCaptureServer{
+		msgsTo: make(chan *pc.Request),
+	}
+
+	stream := boilerplate.PullOutput{
+		Connector_CaptureServer: testSrv,
+	}
+
+	ctx := context.Background()
+
+	// Start up the emitter.
+	emitter := newEmitter(&stream)
+	group, groupCtx := errgroup.WithContext(ctx)
+	group.Go(func() error {
+		return emitter.runtimeAckWorker(groupCtx)
+	})
+	group.Go(func() error {
+		return emitter.emitWorker(groupCtx)
+	})
+
+	// Emit some messages concurrently with many goroutines.
+	numMessages := 50_000
+	half := numMessages / 2
+	ackdMsgs := make(chan string, numMessages)
+	var sent sync.WaitGroup
+
+	for idx := 0; idx < numMessages; idx++ {
+		idx := idx
+		sent.Add(1)
+
+		go func() {
+			m := emitMessage{
+				m: &pubsub.Message{
+					ID:   strconv.Itoa(idx),
+					Data: []byte("{}"),
+				},
+				subcription: "sub",
+				topic:       "topic",
+			}
+
+			runtimeAck, err := emitter.emit(ctx, m)
+			require.NoError(t, err)
+
+			sent.Done()
+			<-runtimeAck       // Simulate ack received from runtime.
+			ackdMsgs <- m.m.ID // Simulate ack sent to PubSub.
+		}()
+	}
+
+	// Wait for all documents to be output from the connector.
+	sent.Wait()
+
+	// Get the set of documents that were output from the connector referenced
+	// by their IDs.
+	gotDocuments := []string{}
+
+	type capturedDoc struct {
+		Meta map[string]string `json:"_meta"`
+	}
+
+	for _, doc := range testSrv.msgsFrom {
+		if doc.Checkpoint != nil {
+			continue
+		}
+
+		var cap capturedDoc
+		require.NoError(t, json.Unmarshal(doc.Captured.DocJson, &cap))
+		gotDocuments = append(gotDocuments, cap.Meta["id"])
+	}
+
+	// Send a runtime acknowledgement for half of emitted checkpoints.
+	testSrv.msgsTo <- &pc.Request{
+		Acknowledge: &pc.Request_Acknowledge{
+			Checkpoints: uint32(half),
+		},
+	}
+
+	// Make sure the acknowledged messages match up to the acknowledged runtime
+	// commits for just the first half.
+	doneCount := 0
+	gotDocs := []string{}
+	for id := range ackdMsgs {
+		doneCount += 1
+		gotDocs = append(gotDocs, id)
+		if doneCount == half {
+			break
+		}
+	}
+	require.ElementsMatch(t, gotDocuments[:half], gotDocs)
+
+	// Send a runtime acknowledgement for the rest of emitted checkpoints.
+	testSrv.msgsTo <- &pc.Request{
+		Acknowledge: &pc.Request_Acknowledge{
+			Checkpoints: uint32(numMessages - half),
+		},
+	}
+
+	// Make sure the acknowledged messages match up to the acknowledged runtime
+	// commits for the second half.
+	doneCount = half
+	gotDocs = []string{}
+	for id := range ackdMsgs {
+		doneCount += 1
+		gotDocs = append(gotDocs, id)
+		if doneCount == numMessages {
+			break
+		}
+	}
+	require.ElementsMatch(t, gotDocuments[half:], gotDocs)
+}
+
+var _ pc.Connector_CaptureServer = &TestCaptureServer{}
+
+type TestCaptureServer struct {
+	msgsTo   chan *pc.Request
+	msgsFrom []pc.Response
+}
+
+func (t *TestCaptureServer) Send(msg *pc.Response) error {
+	t.msgsFrom = append(t.msgsFrom, *msg)
+	return nil
+}
+
+func (t *TestCaptureServer) Recv() (*pc.Request, error) {
+	return <-t.msgsTo, nil
+}
+
+func (t *TestCaptureServer) Context() context.Context {
+	panic("unimplemented")
+}
+
+func (t *TestCaptureServer) RecvMsg(m any) error {
+	panic("unimplemented")
+}
+
+func (t *TestCaptureServer) SendHeader(metadata.MD) error {
+	panic("unimplemented")
+}
+
+func (t *TestCaptureServer) SendMsg(m any) error {
+	panic("unimplemented")
+}
+
+func (t *TestCaptureServer) SetHeader(metadata.MD) error {
+	panic("unimplemented")
+}
+
+func (t *TestCaptureServer) SetTrailer(metadata.MD) {
+	panic("unimplemented")
+}