Eu fiquei de testar a câmera e o microfone antes da apresentação de amanhã.

In Brazilian Portuguese, ficar de + infinitive often means:

• to agree to do something
• to be supposed to do something
• to be left with the task of doing something

So fiquei de testar means something like:

• I agreed to test
• I was supposed to test
• I said I would test

The exact English translation depends on context, but the structure is very common in Portuguese.

Fiquei is the preterite form of ficar, so it refers to a completed past event.

• eu fico = I stay / I become / I am left / I agree (present)
• eu ficava = I used to stay / I would stay / I was staying (imperfect)
• eu fiquei = I stayed / I became / I ended up / I agreed (preterite)

In eu fiquei de testar..., the speaker is referring to a past moment when the responsibility or agreement was established.

Yes. In Portuguese, subject pronouns are often omitted when the verb already makes the subject clear.

So both are natural:

• Eu fiquei de testar a câmera e o microfone...
• Fiquei de testar a câmera e o microfone...

Because fiquei clearly shows I, the pronoun is optional. Including eu can add emphasis or clarity.

Because ficar in this meaning is used with the preposition de.

The pattern is:

• ficar de fazer algo

Examples:

• Fiquei de ligar para ela. = I said I would call her.
• Ele ficou de mandar o arquivo. = He was supposed to send the file.

So fiquei de testar follows that fixed pattern. You generally should learn it as a chunk: ficar de + infinitive.

No. They are related, but not the same.

• fiquei de testar = I agreed / I was supposed to test
• tive que testar = I had to test

The first suggests an arrangement, commitment, or assigned task.
The second suggests obligation or necessity.

So fiquei de testar does not necessarily mean the person actually did it yet—only that they were expected or committed to do it.

Portuguese uses definite articles much more often than English.

So a câmera e o microfone is very natural, even where English might simply say camera and microphone.

The nouns have gender:

• a câmera = feminine
• o microfone = masculine

That is why the articles are different. In Portuguese, you usually learn nouns together with their article.

You can sometimes omit articles in Portuguese, but in this sentence a câmera e o microfone sounds more natural and complete.

Without the articles:

• testar câmera e microfone

it may sound a bit more generic, abbreviated, or technical, depending on context.

In ordinary speech, especially when referring to specific equipment for a presentation, testar a câmera e o microfone is the most natural choice.

Because da is a contraction of:

• de + a = da

The expression is antes de when followed directly by a verb or some structures, but before a feminine noun with an article, contraction is usually used:

• antes da apresentação = before the presentation
• literally: before of-the presentation

This kind of contraction is extremely common in Portuguese:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

De amanhã means of tomorrow or more naturally tomorrow’s.

So:

• a apresentação de amanhã = tomorrow’s presentation / the presentation tomorrow

This is a very common way to identify something by time:

• a reunião de hoje = today’s meeting
• a aula de amanhã = tomorrow’s class

You might also hear a apresentação para amanhã in some contexts, but that can suggest something scheduled for tomorrow rather than simply identifying it as tomorrow’s presentation. In this sentence, de amanhã is the most straightforward and natural choice.

It means before the presentation itself, and that presentation happens tomorrow.

The phrase groups like this:

• antes da [apresentação de amanhã]

So de amanhã modifies apresentação, not antes.

In other words, it does not mean before tomorrow.
It means before tomorrow’s presentation.

E simply means and.

So:

• a câmera e o microfone = the camera and the microphone

There is nothing unusual grammatically here, but English speakers should notice that Portuguese normally repeats the correct article for each noun when their genders differ:

• a câmera e o microfone

You would not say a câmera e microfone in normal careful speech if you mean both specific items.

Yes. Testar is very common in Brazilian Portuguese for checking whether equipment works properly.

Examples:

• testar o microfone
• testar a câmera
• testar a internet
• testar o som

It works much like English to test. In this sentence, it sounds completely natural.

Yes, it is natural.

A Brazilian speaker might also say:

• Fiquei de testar a câmera e o microfone antes da apresentação de amanhã.
• Eu ia testar a câmera e o microfone antes da apresentação de amanhã.
• Eu combinei de testar a câmera e o microfone antes da apresentação de amanhã.
• Eu tinha que testar a câmera e o microfone antes da apresentação de amanhã.

But each alternative changes the nuance a little:

• fiquei de = I agreed / I was supposed to
• ia = I was going to
• combinei de = I arranged/agreed to
• tinha que = I had to

So the original sentence is both grammatical and idiomatic.