What is the test for impeaching a witness in a criminal case?

Appellant relies heavily on People v. Newson, 37 Cal.2d 34, 230 P.2d 618. In that case defendant was charged with murder and a witness for the prosecution was asked on direct examination if at the time of the crime she had seen anyone in a building where the killing occurred. She replied, 'No, I didn't.' Over objection the district attorney was permitted to impeach the witness by showing her prior extra-judicial statements that she had seen defendant in the building at that time. The admission of her prior inconsistent statements was held to be error on the ground that her testimony 'was purely of a negative character * * * neither favorable to one side or the other' and was in no way damaging to the prosecution's case.