What is an ON block?

Question

The art of software testing contains several references to ON-units. Here is an example from the test case design section:

Coverage of requirements can usually satisfy the application. Since each statement belongs to a subpath originating from a branch instruction or from a program entry point, each statement must be executed if each branch direction is executed. However, there are at least three exceptions:

• Programs without any solutions.
• Programs or routines / methods with multiple entry points. This operator can only be executed if the program is entered at a specific entry point.
• Statements in ON units. Passing each branch direction does not necessarily lead to the execution of all ON blocks.

I have not seen the term ON-unit before, and I am having trouble finding a definition in google. What is an ON-unit?

Answer 1

ON-unit is a PL / I exception handling method, like a catch in more modern languages. Therefore, it sounds as if they say that the execution of each code branch (outside ON units) will not necessarily lead to the launch of all processed exceptions (inside ON blocks).