Add unit-tests for card decks (#24791)

* Add unit-tests for card decks

* Fix linter CI comments

* Rename unit-test file due to duplicate filename

* Fix review comments

* Fix unit-test broken after review comment fixing

* Remove blank unit-tests for card-decks

* Use TRUE instead of magic-value 1 in cardshuffle sound call

Co-authored-by: Burzah <116982774+Burzah@users.noreply.github.com>

---------

Co-authored-by: Burzah <116982774+Burzah@users.noreply.github.com>

code/modules/unit_tests/_unit_tests.dm

@@ -2,6 +2,7 @@
 //Keep this sorted alphabetically
 
 #ifdef UNIT_TESTS
+#include "games\test_cards.dm"
 #include "jobs\test_job_globals.dm"
 #include "aicard_icons.dm"
 #include "announcements.dm"

code/modules/unit_tests/games/test_cards.dm

@@ -0,0 +1,30 @@
+/datum/unit_test/card_deck/proc/validate_deck(obj/item/deck/deck)
+	var/list/card_count = list()
+	for(var/datum/playingcard/card in deck.cards)
+		if(card_count[card.name] == null)
+			card_count[card.name] = 1
+		else if(card.name == "Joker")
+			card_count[card.name]++
+		else
+			// duplicate card in deck
+			return FALSE
+
+	if(length(card_count) != 53) // 2 Jokers, so 53 unique cards
+		return FALSE
+	return TRUE
+
+
+/datum/unit_test/card_deck/Run()
+	// setup
+	var/loc = pick(block(run_loc_bottom_left, run_loc_top_right))
+	var/obj/item/deck/cards/cards = new /obj/item/deck/cards(loc)
+	cards.build_decks()
+
+	// is deck proper upon spawning
+	if(!validate_deck(cards))
+		Fail("52 card deck not initialized correctly.")
+
+	// is deck proper after shuffling
+	cards.deckshuffle()
+	if(!validate_deck(cards))
+		Fail("52 card deck broken after shuffling.")