i cleaned up the Java tests suite and enabled JUnit 5. I kept the testing() function because it leads to much shorter lines than assertEquals(Accumul.accum(... and it allows presenting the input in an assertion message.

fixed + upgrade to JUnit 5 + the initial code now compiles + better assertion messages + the tests suite no longer logs to stdout

you under-allocate. your formula is wrong:

char *s = malloc(n / 2 * (n - 3) * sizeof(char) + 1);

for "abc", n = 3, the result string requires "A-Bb-Ccc" = 9 bytes, but your formula allocates 3 / 2 * (3 - 3) + 1 = 1 byte

Oh dear, I remember those!

Merged!

C:

• the initial code does not compile
• it is not explained what kind of pointer to return

fork fixing it (author inactive)

also massively simplifying the tests suite (removal of 200+ lines of preloaded code, among other things)

Fixed.

Im new to this but just noticed theres a tiny issue (not a critical problem at all) where in
public class Accumul
{
public static string Accum(string s)
{
return ""; // your code
}
}
The public static string is written as "String" causing an error.

best one IMO