[tests] use double quote to test \0 as a string

Prevents clang throwing an error, since '\0' is rightfully treated as a
single character.

See this explanation by Stephen J. Butler:
https://lists.macports.org/pipermail/macports-dev/2016-June/033168.html

diff --git a/tests/src/io/test-source.c b/tests/src/io/test-source.c
index abc536c..426bdc9 100644 (file)
--- a/tests/src/io/test-source.c
+++ b/tests/src/io/test-source.c
@@ -70,7 +70,7 @@ int test_wrong_params(void)
   aubio_source_t *s;
 
   if (new_aubio_source(0,    samplerate, hop_size)) return 1;
-  if (new_aubio_source('\0', samplerate, hop_size)) return 1;
+  if (new_aubio_source("\0", samplerate, hop_size)) return 1;
   if (new_aubio_source(uri,          -1, hop_size)) return 1;
   if (new_aubio_source(uri,           0,        0)) return 1;