Question on Oracle Assumption - ISTQB (Foundation Level)

Question

I have seen the following question and the answer on 'Oracle Assumption' for ISTQB Foundation Level exam (Source).

19 The oracle assumption:

• a) is that there is some existing system against which test output may be checked.
• b) is that the tester can routinely identify the correct outcome of a test.
• c) is that the tester knows everything about the software under test.
• d) is that the tests are reviewed by experienced testers.

According to the site, the answer is

- b) is that the tester can routinely identify the correct outcome of a test.

However, the ISTQB glossary says that a Test Oracle is :

A source to determine expected results to compare with the actual result of the software under test. An oracle may be the existing system (for a benchmark), other software, a user manual, or an individual's specialized knowledge, but should not be the code.

Another source says that the Oracle Assumption is :

the assumption that testers will (a) work out expected ourcomes in advance of test execution, as part of test case specification; and (b) avoid doing so by hand wherever possible.

I could not find any other exact definition for Oracle Assumption online.

I have two questions :

1. Is the answer given to the MCQ is correct/incorrect? Why?
2. What is the correct definition of Oracle Assumption for ISTQB - Foundation Level?

Answer 1

In the sample question you posted, answer (b) is correct. The Oracle Assumption is that the tester knows what the expected outcome of a test is based on other information about the system at their disposal. If the question instead read "A Test Oracle:", then the correct answer would have been (a) per the definition you cited from the ISTQB glossary. A Test Oracle is the entity that gives a tester the Oracle Assumption.