test: add unit test for part one

internal/2016/DayFour/code_test.go

@@ -0,0 +1,18 @@
+package dayfour
+
+import "testing"
+
+var testInput = []string{
+	"aaaaa-bbb-z-y-x-123[abxyz]",
+	"a-b-c-d-e-f-g-h-987[abcde]",
+	"not-a-real-room-404[oarel]",
+	"totally-real-room-200[decoy]",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 1514
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}