Improve validator quality in Meltano test tasks to provide user-friendly output

[coderabbitai]

Context

In the Meltano example projects, verification tasks currently use basic shell test commands that only provide exit codes without descriptive messages when validation fails.

Problem

When validators fail, users only see an exit code (!=0) without understanding:

• Which validation failed
• What the expected vs. actual values were
• How to remediate the issue

Desired Improvement

Validators should provide concise, user-facing output that clearly communicates:

• What is being validated
• Why validation failed
• Expected vs. actual values
• Actionable feedback

References

• PR: Meltano: Add example cratedb-to-file #1368
• Comment: Meltano: Add example cratedb-to-file #1368 (comment)
• Requested by: @amotl

Related Files

This improvement is applicable to multiple locations in the repository (detailed analysis will follow in a separate comment).

[coderabbitai]

Repository Analysis: Applicable Locations

I've analyzed the repository to identify where validator quality improvements would be beneficial. Here are the locations with similar patterns:

Files with Shell-Based Validators

1. framework/meltano/cratedb-to-file/pyproject.toml (Lines 36-43)

Current validators:

• File existence checks: test -e output/csv/sys-summits.csv
• File pattern checks: test ! -z "$(ls output/jsonl-gz/sys-summits/sys-summits-*.singer.gz)"
• Record count validations: test $(cat output/csv/sys-summits.csv | wc -l | tr -d ' ') -ge 1605

Issues:

• Silent failures - no indication which file is missing
• No feedback on actual vs. expected record counts
• Cryptic shell syntax for users

2. framework/meltano/file-to-cratedb/pyproject.toml (Lines 30-34)

Current validators:

• Database record count checks: test $(uvx crash -c 'SELECT count(*) FROM melty.continents' --format=json | jq '.[0].count') -eq 7
• Similar pattern for countries table (expecting 250 records)

Issues:

• No output indicating which table has incorrect count
• No display of actual count when validation fails

Recommended Approach

Consider replacing shell test commands with Python scripts or dedicated validation tools that:

1. Print descriptive messages before each check
2. Display expected vs. actual values on failure
3. Provide actionable error messages
4. Maintain the same exit codes for CI/CD compatibility

Example Improvement

Before:

{ cmd = "test -e output/csv/sys-summits.csv" }

After:

{ cmd = "python -c 'import sys; from pathlib import Path; p=Path(\"output/csv/sys-summits.csv\"); sys.exit(0) if p.exists() else print(f\"❌ Missing: {p}\") or sys.exit(1)'" }

Or use a dedicated validation script for cleaner implementation.