Broren min tester tastene igjen, men ingenting skjer.

Both word orders are grammatically correct, but they have slightly different nuances and usage patterns.
• Broren min (“the brother of mine”) puts the noun first, making broren definite and then specifying whose it is. This is the most common spoken form.
• Min bror (“my brother”) is also correct and often found in writing or with adjectives (e.g. min eldre bror).

Tester is the present tense of å teste (“to test”). Norwegian doesn’t have a separate continuous form, so the simple present covers both “tests” and “is testing.” You form it by adding -r to the infinitive stem:
å teste → tester

Tastene is the definite plural of tast (“key,” as on a keyboard). Norwegian noun forms here are:
• Indefinite singular: en tast
• Indefinite plural: taster
• Definite plural: tastene (add -ene)

Adverbs of manner or frequency like igjen usually come after the object or at the end of the clause.
Correct: Broren min tester tastene igjen.
Less common but still possible: Broren min tester igjen tastene.

Yes. Both mean “nothing is happening.” Alternatives:
• Ikke noe skjer. (negation before the noun)
• Det skjer ikke noe. (negation after the verb plus det)

In Norwegian, commas before coordinating conjunctions like men are optional. They’re often used for clarity, especially in longer clauses. Here the comma signals the shift:
Broren min tester tastene igjen, men ingenting skjer.