Learn Hardcore Japanese: kono mae no siken de seiseki wo homerarete, zisin ga demasita. - I was praised for my grades on the last exam, and I gained confidence.

この前 literally means the last time or recently. Here it’s followed by の to modify 試験, so この前の試験 refers to the exam you just took or the most recent exam.

Why is the particle で used after この前の試験?

In this sentence で marks the context or occasion in which something happens. 試験で tells us that the following action (being praised) occurred in connection with that exam, not at a physical location.

What grammar is shown by 成績をほめられて?

This is the passive form of 褒める (to praise). 褒める becomes 褒められる in the passive (‘to be praised’). The ending -て then links this clause to the next one, indicating cause or background.

Why does ほめられて use the て-form instead of the past た-form?

The て-form here connects two clauses to show that the second clause is a result or consequence of the first.
成績をほめられて、自信が出ました
= I was praised for my grades, and as a result I gained confidence.

Why is 自信 followed by が rather than は?

が marks 自信 as the new or focal subject that ‘emerges’ or ‘appears.’ Using は would make it the topic or imply contrast, but here we want to emphasize the sudden appearance of confidence.

What does 自信が出ました literally mean, and could you use another verb instead of 出る?

Literally it means confidence came out. It’s a common way to say you gained confidence. Another frequently used verb is つく, as in 自信がつきました, which also means to acquire confidence. 出る focuses on the feeling emerging, while つく emphasizes acquiring it.

Why is the subject (I or we) omitted in this sentence?

Japanese often omits the subject when it’s clear from context. Here it’s obvious that the speaker is the one who was praised and who gained confidence, so 私が or 僕が is simply left out.