Diagnose a fault you did not plant, using scope tests only

short · 35 min · Objective 3.1

Task

Have somebody else break the guest, or plant three faults and leave them for a week, then diagnose using the scope tests rather than by remembering. The discipline being practised is changing one thing at a time and writing down what each result eliminated, which is what makes a result mean anything.

Steps

  1. Plant three faults on the guest -- a disabled service, a broken file association and a per-user setting change are good candidates -- and record them in a sealed file lab/method/planted.txt that you do not open again until step five.
  2. Work one fault at a time. For each, record the symptom as observed in lab/method/symptoms.csv with header fault,symptom,exact_error,reproducible.
  3. Run the scope tests and record them in lab/method/scope.csv with header fault,another_user,another_machine,conclusion -- the two tests that between them isolate the profile, the account and the machine.
  4. Record each change you made while diagnosing in lab/method/changes.csv with header fault,change,result,eliminated,undone -- one change per row, with whether you reversed it.
  5. Open lab/method/planted.txt and write lab/method/score.csv with header fault,diagnosed_as,actual,correct.

Verify

awk -F, 'NR>1 && NF>=4 {n++} END {print n" symptom(s) recorded"}' lab/method/symptoms.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" scope test(s)"}' lab/method/scope.csv
awk -F, 'NR>1 && NF>=5 {n++} END {print n" change(s) logged"}' lab/method/changes.csv
awk -F, 'NR>1 && $5 ~ /yes/ {n++} END {print n" change(s) undone"}' lab/method/changes.csv
awk -F, 'NR>1 && $4 ~ /no/ {n++} END {print n" wrong diagnos(es) -- this is the point"}' lab/method/score.csv

Three symptoms with exact error text, three scope results, and every unsuccessful change reversed. A changes file where nothing was undone describes a guest that now differs from its starting state in ways nobody understands.

Notes

The exact error text matters more than it seems. "It crashes" and "it closes with no message" are different faults, and the difference is usually the first useful thing in the whole ticket.

This is an independent study companion for CompTIA A+ Core 2 220-1202 and is not produced by or endorsed by CompTIA.