How would you mentor a junior tester struggling to write meaningful test cases?

"Meaningful test cases" is a vague problem; the mentoring approach depends on the underlying gap.

Diagnose by sitting with them through a real story. Ask them to walk you through how they'd test it. Listen for where they get stuck:

• Comprehension gap — they don't fully understand the spec, so they default to obvious cases. Coaching focus: active reading. Highlight ambiguities, write open questions, talk to the PM.
• Technique gap — they understand the feature but only write one happy-path case per requirement. Coaching focus: test design techniques. Walk through EP, BVA, decision tables on a real example, not abstractly.
• Confidence gap — they have ideas but don't write them down because they think they'll be wrong. Coaching focus: psychological safety. "Write 30 weak tests; we'll triage them together. There's no penalty for proposing too much."
• Critical-thinking gap — they take the spec at face value and don't ask "what if". Coaching focus: adversarial mindset. "What if a user does this twice? In a different language? With slow internet?"

Practical mentoring moves: pair, don't lecture (90 minutes of paired test design teaches more than a week of solo struggle); model thinking out loud; give incremental autonomy (week 1 pair, week 2 they design and you review, week 3 peer review with another junior, week 4 solo); review test cases the way you review code; celebrate finding non-obvious cases.

What I'd avoid: giving a textbook of techniques and expecting absorption; doing their work for them; comparing them to peers ("Sara writes more cases than you").

When to escalate: if after a sustained effort the gap doesn't close, talk to the manager. Sometimes the role isn't right; sometimes the team's pace is too fast for an early-career engineer to grow in. That conversation is also part of leadership.