==24934== Invalid read of size 1
==24934==    at 0x4E6ED8A: vfprintf (vfprintf.c:1614)
==24934==    by 0x4E7007F: buffered_vfprintf (vfprintf.c:2254)
==24934==    by 0x4E6AE2D: vfprintf (vfprintf.c:1306)
==24934==    by 0x4E757C7: fprintf (fprintf.c:33)
==24934==    by 0x401160: run_tests (main.c:110)
==24934==    by 0x40108E: main (main.c:77)
==24934==  Address 0x518a040 is 0 bytes inside a block of size 20 free'd
==24934==    at 0x4C245E2: realloc (vg_replace_malloc.c:525)
==24934==    by 0x400C7C: strappend (string_ops.c:12)
==24934==    by 0x401140: run_tests (main.c:108)
==24934==    by 0x40108E: main (main.c:77)