Added ControlRecord decoding tests

Added test validating if we correctly decode Kafka control records.

Signed-off-by: Michal Maslanka <michal@vectorized.io>

control_record_test.go

@@ -1 +1,67 @@
 package sarama
+
+import (
+	"testing"
+)
+
+var (
+	abortTxCtrlRecKey = []byte{
+		0, 0, // version
+		0, 0, // TX_ABORT = 0
+	}
+	abortTxCtrlRecValue = []byte{
+		0, 0, // version
+		0, 0, 0, 10, // coordinator epoch
+	}
+	commitTxCtrlRecKey = []byte{
+		0, 0, // version
+		0, 1, // TX_COMMIT = 1
+	}
+	commitTxCtrlRecValue = []byte{
+		0, 0, // version
+		0, 0, 0, 15, // coordinator epoch
+	}
+	unknownCtrlRecKey = []byte{
+		0, 0, // version
+		0, 128, // UNKNOWN = -1
+	}
+	// empty value for unknown record
+	unknownCtrlRecValue = []byte{}
+)
+
+func testDecode(t *testing.T, tp string, key []byte, value []byte) ControlRecord {
+	controlRecord := ControlRecord{}
+	err := controlRecord.decode(&realDecoder{raw: key}, &realDecoder{raw: value})
+	if err != nil {
+		t.Error("Decoding control record of type " + tp + " failed")
+		return ControlRecord{}
+	}
+	return controlRecord
+}
+
+func assertRecordType(t *testing.T, r *ControlRecord, expected ControlRecordType) {
+	if r.Type != expected {
+		t.Errorf("control record type mismatch, expected: %v, have %v", expected, r.Type)
+	}
+}
+
+func TestDecodingControlRecords(t *testing.T) {
+	abortTx := testDecode(t, "abort transaction", abortTxCtrlRecKey, abortTxCtrlRecValue)
+
+	assertRecordType(t, &abortTx, ControlRecordAbort)
+
+	if abortTx.CoordinatorEpoch != 10 {
+		t.Errorf("abort tx control record coordinator epoch mismatch")
+	}
+
+	commitTx := testDecode(t, "commit transaction", commitTxCtrlRecKey, commitTxCtrlRecValue)
+
+	if commitTx.CoordinatorEpoch != 15 {
+		t.Errorf("commit tx control record coordinator epoch mismatch")
+	}
+	assertRecordType(t, &commitTx, ControlRecordCommit)
+
+	unknown := testDecode(t, "unknown", unknownCtrlRecKey, unknownCtrlRecValue)
+
+	assertRecordType(t, &unknown, ControlRecordUnknown)
+}