Learn Hardcore Russian: Завтра я протестирую новое приложение.

Simple future (one word)
Used with perfective verbs:
- протестировать → я протестирую (I will test / I’ll have tested)
Compound future (буду + infinitive)
Used with imperfective verbs:
- тестировать → я буду тестировать (I will be testing / I’ll be doing testing)

In this sentence, протестирую is perfective, so it forms the future by itself, without буду.

What is the difference between я протестирую and я буду тестировать?

Both refer to the future, but the aspect and nuance differ:

Я протестирую новое приложение.
- perfective
- focuses on one complete action and its result
- roughly: “I will test it (and get it done).”
Я буду тестировать новое приложение.
- imperfective
- focuses on the process or duration
- roughly: “I will be testing it” / “I’ll spend time testing it.”

So if you mean doing the whole test once and finishing it, протестирую is natural.
If you mean working on testing over some period of time, буду тестировать fits better.

Why is it новое приложение and not новый приложение?

Because adjectives in Russian must agree with the noun in:

gender
number
case

The noun приложение is:

neuter
singular
accusative (direct object, but in this case it looks like nominative)

The correct neuter singular (nominative/accusative) ending for новый is новое:

masculine: новый телефон
feminine: новая программа
neuter: новое приложение

So новое приложение is correct agreement: neuter adjective + neuter noun.

What case is новое приложение, and why doesn’t it change its form?

Grammatically, новое приложение is in the accusative case because it is the direct object of the verb:

протестирую что? → новое приложение

However, in Russian:

Inanimate neuter nouns have the same form in nominative and accusative.
Their agreeing adjectives also look the same in these two cases.

So:

Nominative: новое приложение (the new app is good)
Accusative: протестирую новое приложение (I will test the new app)

Same spelling, different case function.

Can the word order change? For example, can I say Я завтра протестирую новое приложение or Я протестирую новое приложение завтра?

Yes, Russian word order is fairly flexible. All of these are grammatically correct:

Завтра я протестирую новое приложение.
Neutral, common: “Tomorrow I will test the new app.”
Я завтра протестирую новое приложение.
Slightly more focus on я (“I, tomorrow, will test the new app”).
Я протестирую новое приложение завтра.
Puts завтра at the end, sometimes with mild emphasis on the time.
Завтра протестирую новое приложение.
More informal, omits я, still clear from the verb form.

The basic meaning stays the same; differences are in rhythm and emphasis, not in grammar.

Can I omit the pronoun я in this sentence?

Yes. Russian often omits subject pronouns when the verb ending clearly shows the person:

Я протестирую новое приложение.
Протестирую новое приложение.

Both are correct and mean the same thing.
Omitting я is especially common in informal speech and when context already makes it obvious who is speaking or acting.

Where is the stress in each word, and how do you roughly pronounce the sentence?

Stresses:

Зáвтра – stress on за: [ZÁV-tra]
я – just ya: [ya]
протести́рую – stress on ти: [pra-ti-STÍR-oo-yu]
но́вое – stress on но: [NÓ-va-ye]
приложе́ние – stress on же: [pri-la-ZHÉ-ni-ye]

A rough phonetic approximation (English-friendly):

ZÁV-tra ya pra-ti-STÍR-oo-yu NÓ-va-ye pri-la-ZHÉ-ni-ye

Is приложение only used for “app”, or does it have other meanings?

Приложение has several meanings depending on context:

Mobile / computer app – the most common modern use:
- новое приложение → a new app
Attachment (to an email or letter):
- файл в приложении → the file in the attachment
Appendix / supplement (to a book, contract, etc.):
- приложение к договору → an appendix to the contract

So it does not always mean “app”; the exact sense comes from context.

Is протестирую a formal or informal word? Are there more natural alternatives?

Протестирую itself is neutral in style and understood by all speakers, especially in IT / tech contexts, where тестировать / протестировать is very common.

However, depending on what you mean, speakers might also say:

проверю новое приложение – “I’ll check the new app”
попробую новое приложение – “I’ll try the new app”
испытаю новое приложение – “I’ll test/put the new app to the test” (more formal/technical or literary)

If you specifically mean software testing, (про)тестировать is perfectly natural.

How does протестировать conjugate in the present/future?

Протестировать is a perfective verb; its present forms are future in meaning (simple future):

я протестирую – I will test
ты протестируешь – you (sg) will test
он / она / оно протестирует – he / she / it will test
мы протестируем – we will test
вы протестируете – you (pl/formal) will test
они протестируют – they will test

The corresponding imperfective verb is тестировать:

я тестирую – I am testing / I test (present)
я буду тестировать – I will be testing (compound future)

Could I say Завтра я тестирую новое приложение to mean the future, like in English “Tomorrow I’m testing the new app”?

It’s grammatically possible, but it sounds less natural and may feel a bit stiff or bookish in everyday speech.

For future meaning, Russian normally prefers:

Завтра я протестирую новое приложение. (perfective → completed event)
Завтра я буду тестировать новое приложение. (imperfective → ongoing process)

Using the present for scheduled future events (like in English: “Tomorrow I’m flying”) is much less common and more restricted in Russian, especially with verbs like тестировать.
So for normal, natural speech, stick to протестирую or буду тестировать.

Why is there no preposition before завтра?

Because завтра is an adverb, not a noun:

завтра – tomorrow
сегодня – today
вчера – yesterday

Adverbs of time like these are used without prepositions:

Я уеду завтра. – I will leave tomorrow.
Мы встретились вчера. – We met yesterday.

So Завтра я протестирую новое приложение needs no preposition before завтра.