refactor(test): use builtin meson test

test/string/str2.c

@@ -2,7 +2,7 @@
 #include <assert.h>
 #include <string.h>
 
-void test_str2(void) {
+int main(void) {
 	string_s *s1 = string_new("Hello, world!", 0);
 	assert(s1 != NULL);
 	string_s *s2 = string_new("Hello, world!", 0);
@@ -27,6 +27,21 @@ void test_str2(void) {
 	assert(string_len(s1) == 50);
 	assert(string_cap(s1) == 64);
 
+	/* Regression: when need == capacity, extend still needs room for '\0'. */
+	string_s *tight_dst = string_new("abc", 4);
+	string_s *tight_src = string_new("d", 0);
+	assert(tight_dst != NULL);
+	assert(tight_src != NULL);
+	assert(string_extend(tight_dst, tight_src) == 0);
+	assert(strcmp(string_cstr(tight_dst), "abcd") == 0);
+	assert(string_cap(tight_dst) >= 5);
+
+	/* Self-extend should be safe and deterministic. */
+	string_s *self = string_new("xy", 0);
+	assert(self != NULL);
+	assert(string_extend(self, self) == 0);
+	assert(strcmp(string_cstr(self), "xyxy") == 0);
+
 	/* Find substring in string */
 	int pos = string_find(s1, " is ");
 	assert(pos == 11);
@@ -34,4 +49,7 @@ void test_str2(void) {
 	string_free(s1);
 	string_free(s2);
 	string_free(extend_me);
+	string_free(tight_dst);
+	string_free(tight_src);
+	string_free(self);
 }