test: add unit tests for CardUtils

[Ayush-Patel-56]

Purpose / Description

Added unit tests for CardUtils. This class had no test coverage before.

Fixes

• Fixes part of [Cleanup]: Add Tests to the code (@NeedsTest) #13283

Approach

Created CardUtilsTest.kt with 7 test cases covering both public methods:

getNotes():

• Empty collection handling
• Single card scenario
• Multiple cards from same note (verifies unique filtering)
• Multiple cards from different notes

getDeckIdForCard():

• Regular deck (oDid = 0)
• Filtered/cram deck (oDid handling)
• Explicit zero oDid edge case

How Has This Been Tested?

Ran unit tests locally:
./gradlew :AnkiDroid:testPlayDebugUnitTest --tests "com.ichi2.anki.CardUtilsTest"
All 7 tests passed with 0 failures.

Learning (optional, can help others)

• Studied existing test patterns from ImportUtilsTest and NoteServiceTest to match project conventions
• Used RobolectricTest base class which provides helper methods like addBasicNote() and addDynamicDeck()
• Learned that filtered decks use the oDid field to store the original deck ID when cards are moved to cram decks

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[david-allison]

Cheers!

In future: It's a huge timesaver to see if code is unused. We've still got... 15 years of cruft (many of which my own) to deal with.

Fun fact:

This code came from 2018, when multiselect in the Card Browser was added: d98f676. It was in Java at the time.

[david-allison]

⚠️ getNotes is unused, and should be deleted

[Ayush-Patel-56]

Done - removed the trivial empty collection test.

[david-allison]

The method in CardUtils should be deleted, not just the test.

[Ayush-Patel-56]

Done, removed getNotes() from CardUtils.kt as well

[david-allison]

Are you sure you're not using an LLM for this? The comments seem very redundant, as they feel t be duplicated in the assertion message

[david-allison]

Suggested change

// Verify oDid is 0 for regular decks

[david-allison]

Suggested change

// In a filtered deck, oDid should be set

[david-allison]

Suggested change

// Move card to a filtered deck

[david-allison]

Suggested change

// Regular deck has oDid = 0