Whenever a character’s action is directly opposed by that of another character, the GM can call for an Opposed Test. Both characters make a test against each other, with the result determining the winner. To make an opposed test, each character rolls a standard test as appropriate to the situation. If only one of the characters succeeds, that character wins. If both succeed, then the characters have tied. If both fail, then nobody wins.
Note that both characters do not have to actually roll the same test: characters making different tests for different actions can still be acting in opposition to one another.
Opposed tests that result in a tie (both characters succeed) are typically broken by comparing Degrees of Success, with the character who has the greater success being the winner. Further ties can be broken by having the characters reroll. Sometimes the GM may rule that the test has simply resulted in a tie and the two characters remain locked against each other until one of them gives up or another opposed test is made.
If a character rolls a Critical Success during an opposed test, they automatically win the contest regardless of their opponent’s Degrees of Success (unless both rolled a critical success, in which case the tie is broken by a roll off).