Cannot run the tests in Isogram exercice

I failed to run the tests for this exercice, the error is a segmentation fault:

make: *** [makefile:22: test] Segmentation fault (core dumped)

The problem is that my solution is working just fine in the programmiz sandbox:

#include <stdio.h>
#include <stdbool.h>
#include <string.h>

bool is_isogram(const char phrase[]) {
    int length = strlen(phrase);
    for (int i = 0; i < length - 1; i++) {
        for (int j = i + 1; j < length; j++) {
            if (phrase[i] == phrase[j]) {return false;}
    return true;

int main() {
    bool boolean = is_isogram("subdermatoglyphic");
    const char* s = (boolean == true) ? "true" : "false";
    return 0;

Can someone confirm that the exercice is still working on his side ?

Take a look at the second test case:

static void test_null(void)
   TEST_IGNORE();   // delete this line to run test

Does that help you getting unstuck?

that is indeed a very good information but not a very nice test ;-)

in other path the presence of this type of test is usually described in the instruction (specifically in Python with the specific error message to write). Could it be added in here as well instead of forcing user to discover it when running the tests ?

Here at Exercism the tests are the specifications, you will have to read them.
You can solve these exercises test by test: Read the test, write code that passes this test, clean your code up, and move on to the next test.

(But I agree that this is not a nice test, I really don’t like it.)