fixing Upcast issues in SubstConstantsSerializerSpecification for v3 trees

Author: kushti

interpreter/shared/src/test/scala/sigma/serialization/SubstConstantsSerializerSpecification.scala

@@ -1,7 +1,7 @@
 package sigma.serialization
 
 import sigma.VersionContext
-import sigma.ast.{ConcreteCollection, EQ, IntArrayConstant, IntConstant, SInt, SubstConstants, Upcast}
+import sigma.ast.{ConcreteCollection, EQ, IntArrayConstant, IntConstant, SInt, SNumericType, SubstConstants, Upcast, Value}
 import sigma.ast.syntax.IntValue
 import sigma.serialization.ErgoTreeSerializer.DefaultSerializer
 import sigmastate.CrossVersionProps
@@ -11,8 +11,12 @@ class SubstConstantsSerializerSpecification extends SerializationSpecification
 
   property("SubstConstant deserialization round trip") {
     forAll(numExprTreeNodeGen) { propRaw =>
-      val prop = if(VersionContext.current.isV3OrLaterErgoTreeVersion && propRaw.tpe.isInstanceOf[SInt.type]) {
-        Upcast(propRaw, SInt)
+      val prop = if(VersionContext.current.isV3OrLaterErgoTreeVersion) {
+        val p = VersionContext.withVersions(2, 2) {
+          // roundtrip to add Upcast nodes needed for v3 trees
+          ValueSerializer.deserialize(ValueSerializer.serialize(propRaw))
+        }
+        Upcast(p.asInstanceOf[Value[SNumericType]], SInt)
       } else {
         propRaw
       }