What test activities occur during requirements engineering process?

The most important activity that the test engineer can conduct during requirements engineering is to ensure that each requirement is testable. A requirement that cannot be tested cannot be guaranteed and, therefore, must be reworked or eliminated. For example, a requirement that says "the system shall be reliable" is untestable. On the other hand, "the MTBF (Mean time between failures) for the system shall be not less than 100 hours of operating time" may be a desirable level of reliability and can be tested; that is, demonstrated to have been satisfied. There are other testing activities that are then conducted during design and coding. [Source]