Is it permissible for a husband to test his wife to ensure her good conduct, or should he leave the matter to God as long as nothing has occurred to indicate improper behavior, especially given concerns about her past actions, her relationships with colleagues, and her inconsistency in prayer?

The fundamental principle regarding Muslims is their safety from indecencies. Allah Almighty has prohibited negative assumptions, spying, and seeking out faults, as stated in His words: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy." The Prophet, peace and blessings be upon him, also forbade spying and seeking out faults, and warned that whoever seeks out the faults of Muslims, Allah will seek out his faults and expose him. The prohibition against seeking out a wife's missteps and suspecting her is further emphasized, as the Prophet, peace and blessings be upon him, forbade a man from coming to his family at night to suspect them or to seek out their missteps. Therefore, as long as you have not seen anything suspicious, treat your family based on what is apparent, protect them, and command them to adhere to the Sharia (definition).