5 cases · about 30 minutes

Find the cause, not a convenient story

Compare possible causes and choose a useful test. Make an investigation plan.

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Cold start · no hints yet Case 1 of 5

Two stories fit the delay

A nightly job runs late after a software release. An unchanged server is late too. That night, the input also tripled. You can inspect logs without changing anything.

What should you write before choosing the next check?

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Write the next-test plan

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Fictional example. Use the structure with your own observations and limits.

What happened, exactly?: A sandbox import rejects three of eight synthetic CSV files. The rejected files use semicolons; the others use commas. All ran on the same parser build.
What two explanations could fit?: Delimiter handling: changing only the delimiter changes the outcome. A missing required field: the failure remains after a delimiter-only change.
What check separates them?: Use one synthetic failing file and an otherwise identical copy with commas. Hold the parser build and required fields fixed in the permitted sandbox.
What would each result mean?: Different outcomes make delimiter handling more plausible. Both fail: the check is inconclusive; inspect required fields. Both pass: the original failure was not reproduced.
When will you stop or escalate?: Stop at the sandbox boundary. Do not replay production records. If the check needs client data or cannot reproduce the failure, ask the owner for the next permitted observation.

What happened, exactly?One observable symptom with a time, system or condition. No root-cause verdict yet.What two explanations could fit?Give each a different predicted observation.What check separates them?Prefer a small, permitted check whose result would change which explanation you favour.What would each result mean?State the expected signals before running the check.When will you stop or escalate?Name an approval boundary, rollback condition or missing evidence.

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The symptom is an observation, with conditions, rather than a root-cause verdict.
Two plausible explanations predict a meaningful difference.
The proposed check can observe that difference within a permitted boundary.
The plan defines inconclusive results and a stop or escalation condition.

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