test: add the loadtime report tool (#9351) (#9364)

This pull request adds the report tool and modifies the loadtime libraries to better support its use.

(cherry picked from commit 8655080a0f)

Co-authored-by: William Banfield <4561443+williambanfield@users.noreply.github.com>

test/loadtime/payload/payload_test.go

@@ -0,0 +1,50 @@
+package payload_test
+
+import (
+	"testing"
+
+	"github.com/tendermint/tendermint/test/loadtime/payload"
+)
+
+const payloadSizeTarget = 1024 // 1kb
+
+func TestSize(t *testing.T) {
+	s, err := payload.MaxUnpaddedSize()
+	if err != nil {
+		t.Fatalf("calculating max unpadded size %s", err)
+	}
+	if s > payloadSizeTarget {
+		t.Fatalf("unpadded payload size %d exceeds target %d", s, payloadSizeTarget)
+	}
+}
+
+func TestRoundTrip(t *testing.T) {
+	const (
+		testConns = 512
+		testRate  = 4
+	)
+	b, err := payload.NewBytes(&payload.Payload{
+		Size:        payloadSizeTarget,
+		Connections: testConns,
+		Rate:        testRate,
+	})
+	if err != nil {
+		t.Fatalf("generating payload %s", err)
+	}
+	if len(b) < payloadSizeTarget {
+		t.Fatalf("payload size in bytes %d less than expected %d", len(b), payloadSizeTarget)
+	}
+	p, err := payload.FromBytes(b)
+	if err != nil {
+		t.Fatalf("reading payload %s", err)
+	}
+	if p.Size != payloadSizeTarget {
+		t.Fatalf("payload size value %d does not match expected %d", p.Size, payloadSizeTarget)
+	}
+	if p.Connections != testConns {
+		t.Fatalf("payload connections value %d does not match expected %d", p.Connections, testConns)
+	}
+	if p.Rate != testRate {
+		t.Fatalf("payload rate value %d does not match expected %d", p.Rate, testRate)
+	}
+}