fix(JSON): a panic could occur when using All+JSON+embeddedOp+$1

Signed-off-by: Maxime Soulé <btik-git@scoubidou.com>

td/td_json.go

@@ -22,6 +22,7 @@ import (
 	"github.com/maxatome/go-testdeep/internal/json"
 	"github.com/maxatome/go-testdeep/internal/location"
 	"github.com/maxatome/go-testdeep/internal/types"
+	"github.com/maxatome/go-testdeep/internal/util"
 )
 
 // forbiddenOpsInJSON contains operators forbidden inside JSON,
@@ -326,8 +327,7 @@ func (s *tdJSONSmuggler) Match(ctx ctxerr.Context, got reflect.Value) *ctxerr.Er
 }
 
 func (s *tdJSONSmuggler) String() string {
-	// Only called by MarshalJSON(), and so only when p.isTestDeeper
-	return s.expectedValue.Interface().(TestDeep).String()
+	return util.ToString(s.expectedValue.Interface())
 }
 
 func (s *tdJSONSmuggler) HandleInvalid() bool {

td/td_json_test.go

@@ -231,6 +231,25 @@ func TestJSON(t *testing.T) {
 			Summary: mustContain("json: unsupported type"),
 		})
 
+	checkError(t, map[string]string{"zip": "pipo"},
+		td.All(td.JSON(`SuperMapOf({"zip":$1})`, "bingo")),
+		expectedError{
+			Path:    mustBe(`DATA`),
+			Message: mustBe("compared (part 1 of 1)"),
+			Got: mustBe(`(map[string]string) (len=1) {
+ (string) (len=3) "zip": (string) (len=4) "pipo"
+}`),
+			Expected: mustBe(`JSON(SuperMapOf(map[string]interface {}{
+       "zip": "bingo",
+     }))`),
+			Origin: &expectedError{
+				Path:     mustBe(`DATA<All#1/1>["zip"]`),
+				Message:  mustBe(`values differ`),
+				Got:      mustBe(`"pipo"`),
+				Expected: mustBe(`"bingo"`),
+			},
+		})
+
 	//
 	// Fatal errors
 	checkError(t, "never tested",