diff --git a/day03/lib/__init__.py b/day03/lib/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/day04/day4.py b/day04/day4.py
index 05ab355..33ae402 100644
--- a/day04/day4.py
+++ b/day04/day4.py
@@ -2,6 +2,9 @@
 Day 4 solution
 """
 
+INPUT = "day04/input.txt"
+INPUT_SMALL = "day04/input-small.txt"
+
 
 def split_numbers(string: str) -> set[int]:
     """
@@ -78,7 +81,7 @@ def grab_data(filename: str) -> list[Card]:
 
 
 def main() -> None:
-    cards: list[Card] = grab_data("day04/input.txt")
+    cards: list[Card] = grab_data(INPUT)
     # Q1
     total_points = sum(card.get_points() for card in cards)
     print(total_points)
diff --git a/day04/input-small.txt b/day04/input-small.txt
new file mode 100644
index 0000000..9bdb874
--- /dev/null
+++ b/day04/input-small.txt
@@ -0,0 +1,6 @@
+Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
diff --git a/day04/tests/__init__.py b/day04/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/day04/tests/test_day4.py b/day04/tests/test_day4.py
new file mode 100644
index 0000000..40da0ea
--- /dev/null
+++ b/day04/tests/test_day4.py
@@ -0,0 +1,25 @@
+from day04.day4 import INPUT_SMALL, Card, Inventory, grab_data, split_numbers
+
+
+def test_split_numbers() -> None:
+    assert split_numbers("6 7 8 9 10") == {6, 7, 8, 9, 10}
+    assert split_numbers("") == set()
+    assert split_numbers("6 6 6 6 6") == {6}
+
+
+def test_grab_data() -> None:
+    cards: list[Card] = grab_data(INPUT_SMALL)
+    assert len(cards) == 6
+    assert cards[0].id == 1 and cards[-1].id == 6
+
+
+def test_card() -> None:
+    card = Card("Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53\n")
+    assert card.get_points() == 8
+    assert card.get_matches() == 4
+
+
+def test_inventory() -> None:
+    cards: list[Card] = grab_data(INPUT_SMALL)
+    inventory: Inventory = Inventory(cards)
+    assert inventory.total_cards() == 30