Перед вебинаром я собираюсь протестировать камеру и микрофон.

Because of the preposition перед.

перед always takes the instrumental case, whether it means:

• in front of (space):
  
  • перед домом – in front of the house
• or before (time):
  
  • перед вебинаром – before the webinar

вебинар (nominative) → вебинаром (instrumental, singular, masculine)

So:

• ✗ перед вебинар – wrong (no case ending)
• ✗ перед вебинара – wrong case (that’s genitive)
• ✓ перед вебинаром – correct (instrumental)

Both mean before the webinar, but they feel slightly different:

• перед вебинаром
  Suggests a time close to the start of the webinar, like right before / shortly before.

  • Перед вебинаром я быстро проверю звук.
    Right before the webinar, I’ll quickly check the sound.

• до вебинара (genitive)
  Just means at any time before the webinar, sometimes emphasizing the period up to that point.

  • Мне нужно подготовить презентацию до вебинара.
    I need to prepare the presentation before the webinar (sometime earlier, not necessarily right before).

In your sentence, перед вебинаром sounds more natural, because testing the camera and microphone is usually done shortly before the event starts.

The verb собираться has two main meanings:

1. To gather / to assemble (people, things)

   • Мы собираемся у входа. – We are gathering at the entrance.

2. To be going to / to intend to do something (when followed by an infinitive)

   • Я собираюсь протестировать камеру. – I’m going to test the camera.
   • Он собирается переехать. – He is going to move.

In your sentence it’s meaning 2: я собираюсь протестировать… = I’m going to test… / I intend to test…

You cannot use собирать here; собирать without -ся only means to collect / to gather things or people, not to be going to do something.

Several verbs could work, but they differ slightly:

• тестировать – to test (imperfective, process/habit)

  • Я буду тестировать камеру. – I will be testing the camera (focus on the process, not necessarily completion).

• протестировать – to test (perfective, one complete action)

  • Implies you will carry out a test and finish it.
  • Fits well for a one-time, practical check before an event.

• проверить – to check (perfective)

  • Also common in this context:
    
    • Я собираюсь проверить камеру и микрофон. – I’m going to check the camera and microphone.

In your sentence, протестировать suggests something like: > I’m going to run a proper test of the camera and microphone (and complete it) before the webinar.

Using the perfective here matches the idea of a single, goal-oriented action done before the webinar starts.

No, those are two different roots:

• протестировать – from тест (test), with prefix про- and suffix -ировать.
  Meaning: to test (devices, systems, etc.).

• протестовать – from протест (protest).
  Meaning: to protest.

So:

• протестировать камеру – to test the camera
• протестовать против решения – to protest against the decision

They only look similar in writing; in meaning (and even stress) they are different.

Both are direct objects of протестировать, so both are in the accusative case.

The forms just look different because of gender and declension patterns:

• камера (feminine, nominative) → камеру (feminine, accusative singular)
  Feminine nouns ending in -а typically change to -у in the accusative.

• микрофон (masculine inanimate, nominative) → микрофон (same form in accusative)
  Inanimate masculine nouns usually have the same form in nominative and accusative.

So the grammar is:

• протестировать (что?) камеру и микрофон – both are direct objects in the accusative case, even though only камера → камеру visibly changes.

Yes, that’s perfectly correct:

• Перед вебинаром я собираюсь протестировать камеру и микрофон.
• Я собираюсь протестировать камеру и микрофон перед вебинаром.

Both are grammatically fine.

The difference is a slight change in emphasis:

• Starting with перед вебинаром sets the time frame first: As for what I’ll do before the webinar...
• Putting it at the end sounds a bit more neutral and “English-like”: you state what you’ll do, then add when.

In everyday speech, the version with перед вебинаром at the end is probably a bit more common, but both are natural.

You can, and it’s grammatically correct, but the nuance changes:

• Я собираюсь протестировать камеру и микрофон перед вебинаром.

  • Intention + completion: I’m going to (I intend to) test them once and get it done before the webinar.

• Я буду тестировать камеру и микрофон перед вебинаром.

  • Future process: I will be testing the camera and microphone before the webinar (focus on the activity, not the result).
  • This could sound a bit like an ongoing or repeated process.

To express a normal one-time check, Russian speakers more often say:

• Я собираюсь протестировать…
• Я проверю… / Я протестирую… перед вебинаром.

So your original sentence is very natural for the typical situation.

Stress and rough pronunciation:

• собираюсь – stress on ра: со-би-РА-юсь
  Approximate to English: sa-bi-RA-yus (with a soft -s at the end, like “syus”).

• протестировать – stress on ти: про-тес-ТИ-ро-вать
  Approximate: pra-tes-TEE-ra-vat’
  (final ть is soft and not fully released; you don’t need to overthink it as a beginner.)

Key point:

• собирАюсь, протестИровать – stress those syllables when you say the sentence.

Russian has two common conjunctions that can both translate as and in English, but they’re not the same:

• и – neutral and, simply adds items:

  • камера и микрофон – camera and microphone (just a list)

• а – and/but in a contrasting sense:

  • У меня есть камера, а микрофона нет.
    I have a camera, but I don’t have a microphone.

In your sentence, you’re just listing two devices you’re going to test, with no contrast, so и микрофон is the correct choice.