diff --git a/internal/2015/DayFour/code_test.go b/internal/2015/DayFour/code_test.go
new file mode 100644
index 0000000..f147b15
--- /dev/null
+++ b/internal/2015/DayFour/code_test.go
@@ -0,0 +1,45 @@
+package dayfour
+
+import (
+	"testing"
+)
+
+func TestPartOne(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []byte
+		expected int
+	}{
+		{"abcdef", []byte("abcdef"), 609043},
+		{"pqrstuv", []byte("pqrstuv"), 1048970},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PartOne(tt.input)
+			if got != tt.expected {
+				t.Errorf("PartOne() = %d, want %d", got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestPartTwo(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []byte
+		expected int
+	}{
+		{"abcdef", []byte("abcdef"), 6742839},
+		{"pqrstuv", []byte("pqrstuv"), 5714438},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PartTwo(tt.input)
+			if got != tt.expected {
+				t.Errorf("PartTwo() = %d, want %d", got, tt.expected)
+			}
+		})
+	}
+}