chore: add ToJSON FromJSON test

Author: tianzhou

internal/plan/plan_test.go

@@ -1,6 +1,9 @@
 package plan
 
 import (
+	"fmt"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -56,6 +59,53 @@ func TestPlanSummary(t *testing.T) {
 	}
 }
 
+func TestPlanJSONRoundTrip(t *testing.T) {
+	testDataDir := "../../testdata/migrate"
+	versions := []string{"v1", "v2", "v3", "v4", "v5"}
+
+	for _, version := range versions {
+		t.Run(fmt.Sprintf("version_%s", version), func(t *testing.T) {
+			planFilePath := filepath.Join(testDataDir, version, "plan.json")
+			
+			// Read the original plan.json file
+			originalJSON, err := os.ReadFile(planFilePath)
+			if err != nil {
+				t.Fatalf("Failed to read %s: %v", planFilePath, err)
+			}
+
+			// First FromJSON: Load plan from JSON
+			plan1, err := FromJSON(originalJSON, "public")
+			if err != nil {
+				t.Fatalf("Failed to parse JSON from %s: %v", planFilePath, err)
+			}
+
+			// First ToJSON: Convert plan back to JSON
+			json1, err := plan1.ToJSON()
+			if err != nil {
+				t.Fatalf("Failed to convert plan to JSON (first): %v", err)
+			}
+
+			// Compare original JSON with first round-trip JSON
+			if string(originalJSON) != json1 {
+				t.Errorf("JSON round-trip failed for %s: original and round-trip JSON differ", version)
+				t.Logf("Original JSON length: %d", len(originalJSON))
+				t.Logf("Round-trip JSON length: %d", len(json1))
+				// For debugging, show first difference
+				minLen := len(originalJSON)
+				if len(json1) < minLen {
+					minLen = len(json1)
+				}
+				for i := 0; i < minLen; i++ {
+					if originalJSON[i] != json1[i] {
+						t.Logf("First difference at position %d: original=%c, round-trip=%c", i, originalJSON[i], json1[i])
+						break
+					}
+				}
+			}
+		})
+	}
+}
+
 func TestPlanToJSON(t *testing.T) {
 	oldSQL := `CREATE TABLE users (
 		id integer NOT NULL