When you are deploying any artifact (page/class/trigger) to any other Salesforce Org, only the artifacts which are being deployed are not validated but it also validates all the other existing artifacts. If any issues in the existing ones, it throws a failure.
Since both the triggers are on Opportunity, when your new test case saves an opportunity, the old Opportunity trigger as well as the new Opportunity trigger will get invoked.
When you are deploying any artifact (page/class/trigger) to any other Salesforce Org, only the artifacts which are being deployed are not validated but it also validates all the other existing artifacts. If any issues in the existing ones, it throws a failure.
Can u post your code here?
Trick
Since both the triggers are on Opportunity, when your new test case saves an opportunity, the old Opportunity trigger as well as the new Opportunity trigger will get invoked.