test: add unit test for part one

internal/2022/DayFour/code_test.go

@@ -0,0 +1,20 @@
+package dayfour
+
+import "testing"
+
+var testInput = []string{
+	"2-4,6-8",
+	"2-3,4-5",
+	"5-7,7-9",
+	"2-8,3-7",
+	"6-6,4-6",
+	"2-6,4-8",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 2
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}