Diagrammatic tests show letters passing through symbols, each of which changes them in a fixed way: reverse the order, move the first letter to the end, shift every letter along the alphabet. You learn the symbols from examples, then use them.
A reliable routine:
- Start with an example that uses one symbol on its own. Compare input and output letter by letter: did the order change, or the letters themselves?
- Write down what each symbol does in a few words.
- Use the examples with two symbols to confirm your notes.
- Apply the symbols in the question from left to right, one at a time, writing the string after each step.
Order matters. Reversing then moving the first letter to the end isn't the same as doing them the other way round, and tests offer both answers. When a symbol is missing, run the known steps first, then ask which symbol turns that result into the output.