Add tests for CountingResponseWriter

internal/helper/countingresponsewriter_test.go

+package helper
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"testing"
+	"testing/iotest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type testResponseWriter struct {
+	data []byte
+}
+
+func (*testResponseWriter) WriteHeader(int)     {}
+func (*testResponseWriter) Header() http.Header { return nil }
+
+func (trw *testResponseWriter) Write(p []byte) (int, error) {
+	trw.data = append(trw.data, p...)
+	return len(p), nil
+}
+
+func TestCountingResponseWriterStatus(t *testing.T) {
+	crw := NewCountingResponseWriter(&testResponseWriter{})
+	crw.WriteHeader(123)
+	crw.WriteHeader(456)
+	assert.Equal(t, 123, crw.Status())
+}
+
+func TestCountingResponseWriterCount(t *testing.T) {
+	crw := NewCountingResponseWriter(&testResponseWriter{})
+	for _, n := range []int{1, 2, 4, 8, 16, 32} {
+		_, err := crw.Write(bytes.Repeat([]byte{'.'}, n))
+		require.NoError(t, err)
+	}
+	assert.Equal(t, int64(63), crw.Count())
+}
+
+func TestCountingResponseWriterWrite(t *testing.T) {
+	trw := &testResponseWriter{}
+	crw := NewCountingResponseWriter(trw)
+
+	testData := []byte("test data")
+	_, err := io.Copy(crw, iotest.OneByteReader(bytes.NewReader(testData)))
+	require.NoError(t, err)
+
+	assert.Equal(t, string(testData), string(trw.data))
+}