fix: allow adding negative expenses to expense reports

[nyomanjyotisa]

Explanation of Change

Allow negative and zero expenses to be added to regular expense reports while continuing to require positive amounts for IOU reports. Add focused coverage for negative, zero, and positive amounts across both report types.

Fixed Issues

$ #98425
PROPOSAL:

Tests

Test case 1 — Expense report:

1. Go to the Self DM.
2. Create one positive and one negative manual expense.
3. Go to Spend > Expenses.
4. Click Create > Create report.
5. Open the report and click Add expenses > Existing expenses.
6. Verify both the positive and negative expenses appear.
7. Add the negative expense.
8. Verify it is added to the report correctly.

Test case 2 — IOU report:

1. Create one positive and one negative unreported expense.
2. Open a 1:1 DM and create an expense to create an IOU report.
3. Open the IOU report.
4. Click More > Add expense > Add existing expense.
5. Verify the positive expense is eligible.
6. Verify the negative expense is not eligible.

• Verify that no errors appear in the JS console

Offline tests

1. Complete the expense setup from the test cases while online.
2. Force the app offline.
3. Repeat the eligibility checks for the expense and IOU reports.
4. Verify the negative expense is available only for the expense report.
5. Add it to the expense report.
6. Go back online.
7. Verify the expense remains in the report.

QA Steps

Same as Tests.

• Verify that no errors appear in the JS console

Console validation: No PR-related console errors were found. The development-only errors reproduced unchanged on the PR base commit and are already documented here.

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If new assets were added or existing ones were modified, I verified that:
  • The assets are optimized and compressed (for SVG files, run npm run compress-svg)
  • The assets load correctly across all supported platforms.
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

Android-pr98627.mp4

Android: mWeb Chrome

Android-mWeb-pr98627.mp4

iOS: Native

ios-pr98627.mp4

iOS: mWeb Safari

ios-mWeb-pr98627.mp4

MacOS: Chrome / Safari

Chrome-pr98627.mp4

[codecov]

Codecov Report

✅ Changes either increased or maintained existing code coverage, great job!

Files with missing lines	Coverage Δ
src/pages/canAddTransactionAmountToReport.ts	100.00% <100.00%> (ø)
src/pages/AddExistingExpense.tsx	0.00% <0.00%> (ø)
... and 6 files with indirect coverage changes

[melvin-bot]

@FitseTLT Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]