test: add unit test for part one

internal/2016/DayFive/code_test.go

@@ -0,0 +1,34 @@
+package dayfive
+
+import (
+	"bytes"
+	"os"
+	"strings"
+	"testing"
+)
+
+var testInput = "abc"
+
+func TestPartOne(t *testing.T) {
+	expected := "18f47a30"
+
+	oldStdout := os.Stdout
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("Failed to create pipe: %v", err)
+	}
+	os.Stdout = w
+
+	PartOne(testInput)
+
+	_ = w.Close()
+	os.Stdout = oldStdout
+
+	var buffer bytes.Buffer
+	_, _ = buffer.ReadFrom(r)
+	got := strings.TrimSpace(buffer.String())
+
+	if got != expected {
+		t.Errorf("PartOne() printed %q, want %q", got, expected)
+	}
+}