code: func (ca *MockCA) IssuePrecertificate(ctx context.Context, _ *caPB.IssueCertificateRequest) (*caPB.IssuePrecertificateResponse, error) {
  	if ca.PEM == nil {
  		return nil, fmt.Errorf("MockCA's PEM field must be set before calling IssueCertificate")
  	}
  	block, _ := pem.Decode(ca.PEM)
  	cert, err := x509.ParseCertificate(block.Bytes)
  	if err != nil {
  		return nil, err
  	}
  	return &caPB.IssuePrecertificateResponse{
  		DER: cert.Raw,
  	}, nil
  }
docs: // IssuePrecertificate is a mock