From 497f421009cde367986ee964d2365697cebb2210 Mon Sep 17 00:00:00 2001
From: yyforyongyu <yy2452@columbia.edu>
Date: Wed, 12 Jul 2023 16:23:29 +0800
Subject: [PATCH] sweep: patch unit test for `feeRateForPreference`

---
 sweep/sweeper.go      |   9 +++-
 sweep/sweeper_test.go | 118 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+), 2 deletions(-)

diff --git a/sweep/sweeper.go b/sweep/sweeper.go
index bf6930945..487ad6cee 100644
--- a/sweep/sweeper.go
+++ b/sweep/sweeper.go
@@ -47,6 +47,10 @@ var (
 	// request from a client whom did not specify a fee preference.
 	ErrNoFeePreference = errors.New("no fee preference specified")
 
+	// ErrFeePreferenceTooLow is returned when the fee preference gives a
+	// fee rate that's below the relay fee rate.
+	ErrFeePreferenceTooLow = errors.New("fee preference too low")
+
 	// ErrExclusiveGroupSpend is returned in case a different input of the
 	// same exclusive group was spent.
 	ErrExclusiveGroupSpend = errors.New("other member of exclusive group " +
@@ -485,9 +489,10 @@ func (s *UtxoSweeper) feeRateForPreference(
 	if err != nil {
 		return 0, err
 	}
+
 	if feeRate < s.relayFeeRate {
-		return 0, fmt.Errorf("fee preference resulted in invalid fee "+
-			"rate %v, minimum is %v", feeRate, s.relayFeeRate)
+		return 0, fmt.Errorf("%w: got %v, minimum is %v",
+			ErrFeePreferenceTooLow, feeRate, s.relayFeeRate)
 	}
 
 	// If the estimated fee rate is above the maximum allowed fee rate,
diff --git a/sweep/sweeper_test.go b/sweep/sweeper_test.go
index 602a5cb8c..dcb7a5792 100644
--- a/sweep/sweeper_test.go
+++ b/sweep/sweeper_test.go
@@ -1,6 +1,7 @@
 package sweep
 
 import (
+	"errors"
 	"os"
 	"reflect"
 	"runtime/debug"
@@ -2239,3 +2240,120 @@ func TestSweeperShutdownHandling(t *testing.T) {
 	)
 	require.Error(t, err)
 }
+
+// TestFeeRateForPreference checks `feeRateForPreference` works as expected.
+func TestFeeRateForPreference(t *testing.T) {
+	t.Parallel()
+
+	dummyErr := errors.New("dummy")
+
+	// Create a test sweeper.
+	s := New(&UtxoSweeperConfig{})
+
+	// errFeeFunc is a mock over DetermineFeePerKw that always return the
+	// above dummy error.
+	errFeeFunc := func(_ chainfee.Estimator, _ FeePreference) (
+		chainfee.SatPerKWeight, error) {
+
+		return 0, dummyErr
+	}
+
+	// Set the relay fee rate to be 1.
+	s.relayFeeRate = 1
+
+	// smallFeeFunc is a mock over DetermineFeePerKw that always return a
+	// fee rate that's below the relayFeeRate.
+	smallFeeFunc := func(_ chainfee.Estimator, _ FeePreference) (
+		chainfee.SatPerKWeight, error) {
+
+		return s.relayFeeRate - 1, nil
+	}
+
+	// Set the max fee rate to be 1000 sat/vb.
+	s.cfg.MaxFeeRate = 1000
+
+	// largeFeeFunc is a mock over DetermineFeePerKw that always return a
+	// fee rate that's larger than the MaxFeeRate.
+	largeFeeFunc := func(_ chainfee.Estimator, _ FeePreference) (
+		chainfee.SatPerKWeight, error) {
+
+		return s.cfg.MaxFeeRate.FeePerKWeight() + 1, nil
+	}
+
+	// validFeeRate is used to test the success case.
+	validFeeRate := (s.cfg.MaxFeeRate.FeePerKWeight() + s.relayFeeRate) / 2
+
+	// normalFeeFunc is a mock over DetermineFeePerKw that always return a
+	// fee rate that's within the range.
+	normalFeeFunc := func(_ chainfee.Estimator, _ FeePreference) (
+		chainfee.SatPerKWeight, error) {
+
+		return validFeeRate, nil
+	}
+
+	testCases := []struct {
+		name              string
+		feePref           FeePreference
+		determineFeePerKw feeDeterminer
+		expectedFeeRate   chainfee.SatPerKWeight
+		expectedErr       error
+	}{
+		{
+			// When the fee preference is empty, we should see an
+			// error.
+			name:        "empty fee preference",
+			feePref:     FeePreference{},
+			expectedErr: ErrNoFeePreference,
+		},
+		{
+			// When an error is returned from the fee determinor,
+			// we should return it.
+			name:              "error from DetermineFeePerKw",
+			feePref:           FeePreference{FeeRate: 1},
+			determineFeePerKw: errFeeFunc,
+			expectedErr:       dummyErr,
+		},
+		{
+			// When DetermineFeePerKw gives a too small value, we
+			// should return an error.
+			name:              "fee rate below relay fee rate",
+			feePref:           FeePreference{FeeRate: 1},
+			determineFeePerKw: smallFeeFunc,
+			expectedErr:       ErrFeePreferenceTooLow,
+		},
+		{
+			// When DetermineFeePerKw gives a too large value, we
+			// should cap it at the max fee rate.
+			name:              "fee rate above max fee rate",
+			feePref:           FeePreference{FeeRate: 1},
+			determineFeePerKw: largeFeeFunc,
+			expectedFeeRate:   s.cfg.MaxFeeRate.FeePerKWeight(),
+		},
+		{
+			// When DetermineFeePerKw gives a sane fee rate, we
+			// should return it without any error.
+			name:              "success",
+			feePref:           FeePreference{FeeRate: 1},
+			determineFeePerKw: normalFeeFunc,
+			expectedFeeRate:   validFeeRate,
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			// Attach the mocked method.
+			s.cfg.DetermineFeePerKw = tc.determineFeePerKw
+
+			// Call the function under test.
+			feerate, err := s.feeRateForPreference(tc.feePref)
+
+			// Assert the expected feerate.
+			require.Equal(t, tc.expectedFeeRate, feerate)
+
+			// Assert the expected error.
+			require.ErrorIs(t, err, tc.expectedErr)
+		})
+	}
+}