wallet/size test: add TestEstimateVirtualSize

This commit adds a test for EstimateVirtualSize. Currently three
test transactions are added:
    - 1 P2WPKH inputs + 2 P2PKH outputs
    - 1 P2SH-P2WPKH inputs + 2 P2PKH outputs
    - 1 P2WPKH inputs + 1 P2PKH output + 1 P2WPKH change output

wallet/internal/txsizes/size_test.go

@@ -1,6 +1,8 @@
 package txsizes_test
 
 import (
+	"bytes"
+	"encoding/hex"
 	"testing"
 
 	"github.com/roasbeef/btcd/wire"
@@ -60,3 +62,94 @@ func TestEstimateSerializeSize(t *testing.T) {
 		}
 	}
 }
+
+func TestEstimateVirtualSize(t *testing.T) {
+
+	type estimateVSizeTest struct {
+		tx             func() (*wire.MsgTx, error)
+		p2wkhIns       int
+		nestedP2wkhIns int
+		change         bool
+		result         int
+	}
+
+	// TODO(halseth): add tests for more combination out inputs/outputs.
+	tests := []estimateVSizeTest{
+		// Spending P2WPKH to two outputs. Example adapted from example in BIP-143.
+		{
+			tx: func() (*wire.MsgTx, error) {
+				txHex := "01000000000101ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a0100000000ffffffff02202cb206000000001976a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac9093510d000000001976a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac0247304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee0121025476c2e83188368da1ff3e292e7acafcdb3566bb0ad253f62fc70f07aeee635711000000"
+				b, err := hex.DecodeString(txHex)
+				if err != nil {
+					return nil, err
+				}
+				tx := &wire.MsgTx{}
+				err = tx.Deserialize(bytes.NewReader(b))
+				if err != nil {
+					return nil, err
+				}
+
+				return tx, nil
+			},
+			p2wkhIns: 1,
+			result:   147,
+		},
+		{
+			// Spending P2SH-P2WPKH to two outputs. Example adapted from example in BIP-143.
+			tx: func() (*wire.MsgTx, error) {
+				txHex := "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"
+				b, err := hex.DecodeString(txHex)
+				if err != nil {
+					return nil, err
+				}
+				tx := &wire.MsgTx{}
+				err = tx.Deserialize(bytes.NewReader(b))
+				if err != nil {
+					return nil, err
+				}
+
+				return tx, nil
+			},
+			nestedP2wkhIns: 1,
+			result:         170,
+		},
+		{
+			// Spendin P2WPKH to on output, adding one change output. We reuse
+			// the transaction spending to two outputs, removing one of them.
+			tx: func() (*wire.MsgTx, error) {
+				txHex := "01000000000101ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a0100000000ffffffff02202cb206000000001976a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac9093510d000000001976a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac0247304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee0121025476c2e83188368da1ff3e292e7acafcdb3566bb0ad253f62fc70f07aeee635711000000"
+				b, err := hex.DecodeString(txHex)
+				if err != nil {
+					return nil, err
+				}
+				tx := &wire.MsgTx{}
+				err = tx.Deserialize(bytes.NewReader(b))
+				if err != nil {
+					return nil, err
+				}
+
+				// Only keep the first output.
+				tx.TxOut = []*wire.TxOut{tx.TxOut[0]}
+				return tx, nil
+			},
+			p2wkhIns: 1,
+			change:   true,
+			result:   144,
+		},
+	}
+
+	for _, test := range tests {
+		tx, err := test.tx()
+		if err != nil {
+			t.Fatalf("unable to get test tx: %v", err)
+		}
+
+		est := EstimateVirtualSize(0, test.p2wkhIns,
+			test.nestedP2wkhIns, tx.TxOut, test.change)
+
+		if est != test.result {
+			t.Fatalf("expected estimated vsize to be %d, "+
+				"instead got %d", test.result, est)
+		}
+	}
+}