private static void addPrototypeTest(
     @NotNull JstdTestCaseStructure testCaseStructure,
     @Nullable JSExpression rightAssignmentOperand,
     @NotNull JSDefinitionExpression wholeLeftDefExpr) {
   JSReferenceExpression wholeLeftRefExpr =
       ObjectUtils.tryCast(wholeLeftDefExpr.getExpression(), JSReferenceExpression.class);
   LeafPsiElement testMethodLeafPsiElement = null;
   if (wholeLeftRefExpr != null) {
     testMethodLeafPsiElement =
         ObjectUtils.tryCast(wholeLeftRefExpr.getReferenceNameElement(), LeafPsiElement.class);
   }
   if (testMethodLeafPsiElement != null
       && testMethodLeafPsiElement.getElementType() == JSTokenTypes.IDENTIFIER) {
     JSFunctionExpression jsFunctionExpression =
         JsPsiUtils.extractFunctionExpression(rightAssignmentOperand);
     JstdTestStructure jstdTestStructure =
         JstdTestStructure.newPrototypeBasedTestStructure(
             wholeLeftDefExpr, testMethodLeafPsiElement, jsFunctionExpression);
     if (jstdTestStructure != null) {
       testCaseStructure.addTestStructure(jstdTestStructure);
     }
   }
 }