الفني يختبر الإشارة.

A careful MSA pronunciation with full case endings is:

al-fanniyyu yakhtabiru al-ishārata

A very common pause-style pronunciation, with the final case vowels not pronounced, is closer to:

al-fannī yakhtabir al-ishārah

If you want the fully vowelled Arabic, it is:

الفَنِّيُّ يَخْتَبِرُ الإِشَارَةَ

الـ is the Arabic definite article, equivalent to the in English.

So:

• فني = a technician / technical
• الفني = the technician

and:

• إشارة = a signal / indication
• الإشارة = the signal

Unlike English, Arabic attaches the directly to the beginning of the noun.

This is very common in Arabic. A word that is originally an adjective can also be used as a noun when the context makes the role clear.

فني can mean:

• technical
• artistic in some contexts
• technician as a person

Here, because it is referring to a person doing the action, الفني is understood as the technician.

So this is basically a noun-like use of an adjective.

يختبر is a present/imperfect verb in the 3rd person masculine singular.

It means:

• he tests
• he is testing

Why 3rd person masculine singular?

Because the subject is الفني = the technician, which is singular and masculine.

So the verb form matches that subject.

It can mean either one.

In Arabic, the imperfect verb often covers both:

• the simple present: he tests
• the present progressive: he is testing

The exact meaning depends on context.

So الفني يختبر الإشارة could mean either:

• The technician tests the signal
• The technician is testing the signal

Both orders are possible in MSA.

This sentence uses subject–verb–object order:

• الفني = subject
• يختبر = verb
• الإشارة = object

So:

الفني يختبر الإشارة

But Arabic also very commonly uses verb–subject–object order:

يختبر الفني الإشارة

Both are grammatical. The choice depends on style, emphasis, and context.

In fully vocalized MSA, the sentence is:

الفَنِّيُّ يَخْتَبِرُ الإِشَارَةَ

The endings are:

• الفنيُّ → nominative, because it is the subject
• يختبرُ → indicative, the normal mood for a present-tense verb in a plain statement
• الإشارةَ → accusative, because it is the direct object

So the sentence literally shows the grammatical roles through these endings.

Because it is the direct object of the verb يختبر.

The technician is doing the action of testing, and the signal is the thing being tested.

In Arabic, direct objects are normally in the accusative case.

So:

• الفنيُّ = the doer of the action
• الإشارةَ = the thing receiving the action

يختبر comes from the root خ ب ر.

In this form, the verb is اختبر in the past tense, and يختبر in the present/imperfect.

This is commonly identified as Form VIII.

So you can think of it as:

• past: اختبر = he tested
• present: يختبر = he tests / he is testing

Knowing the root can help you connect it with related words involving knowledge, experience, or testing.

Because neither ف in الفني nor the initial sound of الإشارة causes assimilation of the article.

In Arabic, the ل in الـ is pronounced with so-called moon letters, but it assimilates with sun letters.

Here:

• ف is a moon letter, so you say al-fannī
• إشارة begins with a hamza sound, so the l is also pronounced: al-ishārah

So you do not merge the l into the next sound in either word.

If the technician were female:

الفنية تختبر الإشارة
The female technician is testing the signal.

If the technicians were plural masculine:

الفنيون يختبرون الإشارة
The technicians are testing the signal.

If they were plural feminine:

الفنيات يختبرن الإشارة
The female technicians are testing the signal.

This shows how the verb changes to match the subject in gender and number.