The 178th mitzvah is that we are commanded to testify before judges regarding any information we might have. Regardless of whether it will cause damage to the subject of the testimony or save him monetarily or physically, we are required to testify and notify the judges of whatever we have seen or heard.

Our Sages proved that it is required to give testimony from G‑d's statement1 (exalted be He), "If he was a witness who saw or knew [something, if he does not testify, he must bear his guilt]."

One who transgresses this mitzvah by withholding testimony is guilty of a grave sin, as G‑d said2 (exalted be He), "If he does not testify, he must bear his guilt." This is in general. But if he withheld testimony in a financial dispute, and swore falsely that he knew no testimony, he must bring a korban oleh v'yored, as described in Scripture3 in accordance with the conditions given in tractate Shavuos.4

The details of this mitzvah are explained in tractates Sanhedrin5 and Shavuos.6