chanfunding: match error string when testing CoinSelectSubtractFees

lnwallet/chanfunding/coin_select_test.go

@@ -2,6 +2,7 @@ package chanfunding
 
 import (
 	"encoding/hex"
+	"regexp"
 	"testing"
 
 	"github.com/btcsuite/btcd/wire"
@@ -209,6 +210,12 @@ func TestCoinSelectSubtractFees(t *testing.T) {
 	const dustLimit = btcutil.Amount(1000)
 	const dust = btcutil.Amount(100)
 
+	// removeAmounts replaces any amounts in string with "<amt>".
+	removeAmounts := func(s string) string {
+		re := regexp.MustCompile(`[[:digit:]]+\.?[[:digit:]]*`)
+		return re.ReplaceAllString(s, "<amt>")
+	}
+
 	type testCase struct {
 		name       string
 		highFee    bool
@@ -218,7 +225,7 @@ func TestCoinSelectSubtractFees(t *testing.T) {
 		expectedInput      []btcutil.Amount
 		expectedFundingAmt btcutil.Amount
 		expectedChange     btcutil.Amount
-		expectErr          bool
+		expectErr          string
 	}
 
 	testCases := []testCase{
@@ -279,7 +286,8 @@ func TestCoinSelectSubtractFees(t *testing.T) {
 			},
 			spendValue: fundingFee(feeRate, 1, false) + dust,
 
-			expectErr: true,
+			expectErr: "output amount(<amt> BTC) after subtracting " +
+				"fees(<amt> BTC) below dust limit(<amt> BTC)",
 		},
 		{
 			// After subtracting fees, the resulting change output
@@ -355,7 +363,7 @@ func TestCoinSelectSubtractFees(t *testing.T) {
 			},
 			spendValue: 5 * fundingFee(highFeeRate, 1, false),
 
-			expectErr: true,
+			expectErr: "fee <amt> BTC on total output value <amt> BTC",
 		},
 	}
 
@@ -371,19 +379,28 @@ func TestCoinSelectSubtractFees(t *testing.T) {
 			selected, localFundingAmt, changeAmt, err := CoinSelectSubtractFees(
 				feeRate, test.spendValue, dustLimit, test.coins,
 			)
-			if !test.expectErr && err != nil {
-				t.Fatalf(err.Error())
+			if err != nil {
+				switch {
+				case test.expectErr == "":
+					t.Fatalf(err.Error())
+
+				case test.expectErr != removeAmounts(err.Error()):
+					t.Fatalf("expected error '%v', got '%v'",
+						test.expectErr,
+						removeAmounts(err.Error()))
+
+				// If we got an expected error, there is
+				// nothing more to test.
+				default:
+					return
+				}
 			}
 
-			if test.expectErr && err == nil {
+			// Check that there was no expected error we missed.
+			if test.expectErr != "" {
 				t.Fatalf("expected error")
 			}
 
-			// If we got an expected error, there is nothing more to test.
-			if test.expectErr {
-				return
-			}
-
 			// Check that the selected inputs match what we expect.
 			if len(selected) != len(test.expectedInput) {
 				t.Fatalf("expected %v inputs, got %v",