look for the difference in these two lines:

[[M: 37 B: 5 C: 4][][M: 100 B: 14 C: 11]...
[[M: 37 B: 5 C: 4][, ][M: 100 B: 14 C: 11]...

thx a lot, now it's much clear

No problem for me. I added in "Your example test cases":

assertEquals("[[M: 9991 B: 1427 C: 1110]]", Carboat.howmuch(9990, 10000));

and the tests passed. But if I put

assertEquals("[[M: 9990 B: 1427 C: 1110]]", Carboat.howmuch(9990, 10000));

which is false because of 9990 instead of 9991

I'm getting

expected:<[[M: 999[0] B: 1427 C: 1110]]> but was:<[[M: 999[1] B: 1427 C: 1110]]>

the extra brackets which you found weird are there to show where the strings are different! Hope that will help you!

runnig my code in IDE with howmuch(9990, 10000) gives [[M: 9991 B: 1427 C: 1110]] but submitting the same code in CW gives:
BasicTests(CarboatTest)
****** Basic tests ******
expected:<[[[M: 9991 B: 1427 C: 1110]]]> but was:<[[]]>

=(

task for kata is cool but output format should be reconsidered since there are strange issues with those braces...

thanks, I'll check it..but then probably Instructions should be updated so they are consistent with Unit test to minimize confusion?

Java tests are correctly written but for a reason I don't know the output of square brackets in CW is weird:-(

besides Kata Instructions state: howmuch(1, 100) => [["M: 37", "B: 5", "C: 4"], ["M: 100", "B: 14", "C: 11"]]

Note in "Your example test cases" and "Your solution" that in Java the function returns a string which kind of mimics an array.
In "Your example test cases" you could read:

assertEquals("[[M: 37 B: 5 C: 4][M: 100 B: 14 C: 11]]", 
				Carboat.howmuch(1, 100));

which, as you can see is correctly written.

Many Codewarriors passed the kata in Java without problems. I just tried myself and everything went fine.

Java test says: expected:<[[M: 37[ B: 5 C: 4][M: 100 B: 14] C: 11]]>
guys, what?? what is that format with square brace after "37"?
besides Kata Instructions state:
howmuch(1, 100) => [["M: 37", "B: 5", "C: 4"], ["M: 100", "B: 14", "C: 11"]]

Format of output is completely different - double quotes, less braces. Probably Java tests should be fixed =(

that was an infinite loop due to wrong condition ;(

The general workaround is to write faster code.
Although for this kata, I can't really imagine an answer which is too inefficient.
Infinite loop/recursion is more likely.

Could you post your code here? (Mark it as spoiler)

.length points to just a field of array object. No calculations are even beeing performed at this point.
The much worse is concatenating strings in a cycle. That's a very bad practice

Process was terminated. It took longer than 10000ms to complete
well ((((( what's workaround here?