test(overlay): add coverage for overlay rendering

[frittlechasm]

Pull Request

Description

Adds test coverage for the internal/render/tui/overlay package as part of #63.

The tests cover the package's current behavior without changing production code. Found some issues that I will raise another PR for 100% coverage.

Changes Made

• Added tests for centered, left-aligned, right-aligned, and bottom-right overlays
• Added tests for padding, coordinate clamping, shadows, and custom whitespace
• Added tests for ANSI-styled text and Unicode display widths
• Increased package test coverage from 0% to 98.5%

Testing

go test -cover ./internal/render/tui/overlay

• Tested locally with example workflows
• Added new tests (if applicable)
• Tested with different filters, output, etc...

Checklist

• I have starred the repository
• My code follows the project's code style
• I have updated the documentation (README, cli-flags, etc...)
• My changes generate no new warnings
• I have tested my changes in a real workflow
• All tests pass locally

Greptile Summary

This PR adds coverage for overlay placement and rendering helpers. One non-blocking coverage gap remains: the shadow test does not verify the shadow's full horizontal geometry, so some visible rendering regressions would still pass.

Confidence Score: 4/5

Safe to merge from a product-safety perspective; the remaining concern affects regression protection rather than runtime behavior.

The only finding is a verified, non-blocking test-coverage gap.

Files Needing Attention: internal/render/tui/overlay/overlay_test.go

T-Rex Logs

What T-Rex did

• T-Rex produced a proof for the posted P2 finding and linked it to the corresponding review comment.
• T-Rex produced a second P2 finding proof for another review comment and prepared its artifacts for reviewer inspection.
• T-Rex ran contract-validation tests for rendering baseline and several mutants; the baseline and two mutants passed, while one variant's result was explained by overlay clamping.

_{Ran code and verified through T-Rex}

Comments Outside Diff (1)

1. General comment

   Shadow test accepts incorrect horizontal offset and width

   • Bug
     • TestPlaceOverlayWithShadow checks the exact first line but only requires that lines[1] contain at least one ░; it does not check the shadow rune's column or count, and it does not assert the final line. Focused temporary-copy mutations shifting the shadow left and increasing its width both passed the current test despite visibly changing the rendered geometry.
   • Cause
     • The test uses strings.Contains(lines[1], "░") at lines 136-138 instead of asserting the complete expected shadow geometry or ANSI-stripped line contents across all relevant rows.
   • Fix
     • Assert the full expected geometry after stripping ANSI styling (for this input: first row X .., second row ░.., final row ....), or assert explicit shadow positions/counts and unchanged final row.

   _{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "test(overlay): add coverage for overlay ..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

[greptile-apps]

Protect Shadow Geometry

This non-blocking test only checks whether the second row contains a shadow rune, not its column or width, and it does not assert the final row. A shifted or wider shadow can therefore change the rendered overlay while this test still passes, reducing the value of the new regression coverage. Assert the ANSI-stripped complete output, or explicitly check each shadow row and rune position.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

Artifacts

Evidence from the check

• A non-destructive script copies the repository to a temporary directory, runs the baseline test, then runs vertical-extent, horizontal-offset, and width mutants; it shows which broken geometries the existing test accepts.

Command output from the check

• Captured output from executing the focused mutation script shows baseline success and that left-offset and wider-shadow mutants still pass, confirming the coverage gap.

_{Ran code and verified through T-Rex}

[frittlechasm]

tried to fix this in 186e6a3 with help from Codex & Claude