paymentsdb: added unit test for computePaymentStatusFromResolutions

diff --git a/payments/db/sql_store_test.go b/payments/db/sql_store_test.go
new file mode 100644
index 0000000..0f4f310
--- /dev/null
+++ b/payments/db/sql_store_test.go
@@ -0,0 +1,229 @@
+//go:build test_db_sqlite || test_db_postgres
+
+package paymentsdb
+
+import (
+	"database/sql"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestComputePaymentStatus tests the SQL to domain type conversion logic in
+// computePaymentStatusFromResolutions. This is a pure unit test with no
+// database interaction. However the function is only used in the SQL store and
+// used sql data types so we test it in a sql specific file.
+func TestComputePaymentStatus(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name            string
+		resolutionTypes []sql.NullInt32
+		failReason      sql.NullInt32
+		expectedStatus  PaymentStatus
+		expectError     bool
+	}{
+		{
+			name: "all NULL resolutions means in-flight",
+			resolutionTypes: []sql.NullInt32{
+				{Valid: false}, // NULL = in-flight
+				{Valid: false},
+			},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusInFlight,
+		},
+		{
+			name: "settled resolution without fail reason",
+			resolutionTypes: []sql.NullInt32{{
+				Int32: int32(HTLCAttemptResolutionSettled),
+				Valid: true,
+			}},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusSucceeded,
+		},
+		{
+			name: "failed resolution without fail reason",
+			resolutionTypes: []sql.NullInt32{{
+				Int32: int32(HTLCAttemptResolutionFailed),
+				Valid: true,
+			}},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusInFlight,
+		},
+		{
+			name: "failed resolution with fail reason",
+			resolutionTypes: []sql.NullInt32{{
+				Int32: int32(HTLCAttemptResolutionFailed),
+				Valid: true,
+			}},
+			failReason: sql.NullInt32{
+				Int32: int32(FailureReasonNoRoute),
+				Valid: true,
+			},
+			expectedStatus: StatusFailed,
+		},
+		{
+			name: "mixed: in-flight and settled",
+			resolutionTypes: []sql.NullInt32{
+				{Valid: false}, // in-flight
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+			},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusInFlight,
+		},
+		{
+			name: "mixed: in-flight and failed",
+			resolutionTypes: []sql.NullInt32{
+				{Valid: false}, // in-flight
+				{
+					Int32: int32(
+						HTLCAttemptResolutionFailed,
+					),
+					Valid: true,
+				},
+			},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusInFlight,
+		},
+		{
+			name: "mixed: settled and failed",
+			resolutionTypes: []sql.NullInt32{
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionFailed,
+					),
+					Valid: true,
+				},
+			},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusSucceeded,
+		},
+		{
+			name: "no resolutions, no fail reason, " +
+				"means initiated",
+			resolutionTypes: []sql.NullInt32{},
+			failReason:      sql.NullInt32{Valid: false},
+			expectedStatus:  StatusInitiated,
+		},
+		{
+			name: "no resolutions with fail reason, " +
+				"means failed",
+			resolutionTypes: []sql.NullInt32{},
+			failReason: sql.NullInt32{
+				Int32: int32(FailureReasonNoRoute),
+				Valid: true,
+			},
+			expectedStatus: StatusFailed,
+		},
+		{
+			name: "unknown resolution type returns error",
+			resolutionTypes: []sql.NullInt32{
+				{Int32: 999, Valid: true}, // invalid type
+			},
+			failReason:  sql.NullInt32{Valid: false},
+			expectError: true,
+		},
+		{
+			name: "all three states: in-flight, settled, failed",
+			resolutionTypes: []sql.NullInt32{
+				{
+					Valid: false, // in-flight
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionFailed,
+					),
+					Valid: true,
+				},
+			},
+			failReason: sql.NullInt32{
+				Int32: int32(FailureReasonTimeout),
+				Valid: true,
+			},
+			expectedStatus: StatusInFlight,
+		},
+		{
+			name: "multiple settled HTLCs",
+			resolutionTypes: []sql.NullInt32{
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionSettled,
+					),
+					Valid: true,
+				},
+			},
+			failReason:     sql.NullInt32{Valid: false},
+			expectedStatus: StatusSucceeded,
+		},
+		{
+			name: "multiple failed HTLCs with fail reason",
+			resolutionTypes: []sql.NullInt32{
+				{
+					Int32: int32(
+						HTLCAttemptResolutionFailed,
+					),
+					Valid: true,
+				},
+				{
+					Int32: int32(
+						HTLCAttemptResolutionFailed,
+					),
+					Valid: true,
+				},
+			},
+			failReason: sql.NullInt32{
+				Int32: int32(FailureReasonNoRoute),
+				Valid: true,
+			},
+			expectedStatus: StatusFailed,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			status, err := computePaymentStatusFromResolutions(
+				tc.resolutionTypes, tc.failReason,
+			)
+
+			if tc.expectError {
+				require.Error(t, err)
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tc.expectedStatus, status,
+				"got %s, want %s", status, tc.expectedStatus)
+		})
+	}
+}