Add more tests of strings

test/strings.c

 #include <utils/strings.h>
 #include <criterion/criterion.h>
 
+Test(strings, strupper) {
+	char *test = malloc(sizeof(char) * 5);
+	strcpy(test, "test");
+	test = strupper(test, test);
+	cr_expect_str_eq(test, "TEST", "simple test of upper");
+
+	strcpy(test, "TrOu");
+	test = strupper(test, test);
+	cr_expect_str_eq(test, "TROU", "Other test of upper");
+	free(test);
+}
+
+Test(strings, strlower) {
+	char *test = malloc(sizeof(char) * 5);
+	strcpy(test, "TEST");
+	test = strlower(test, test);
+	cr_expect_str_eq(test, "test", "simple test of lower");
+
+	strcpy(test, "TrOu");
+	test = strlower(test, test);
+	cr_expect_str_eq(test, "trou", "Other test of lower");
+	free(test);
+}
+
 Test(strings, strreverse) {
 	char *test = malloc(sizeof(char) * 5);
 	strcpy(test, "test");
 	test = strreverse(test, test);
-    cr_expect(strcmp(test, "tset") == 0, "simple test of reverse");
+	cr_expect_str_eq(test, "tset", "simple test of reverse");
+
+	test = realloc(test, sizeof(char) * 6);
+	strcpy(test, "kayak");
+	test = strreverse(test, test);
+	cr_expect_str_eq(test, "kayak", "palindrome test of reverse");
 	free(test);
 }