Update test57.c per a suggestion by @mark-summerfield

Use a non-null `someaddr`, and use more thorough asserts instead
of a single printf so that we get a bit more test coverage here.

doc/userguide.txt

@@ -805,7 +805,7 @@ Here is a simple example where a structure has a pointer member, called `key`.
 
 .A pointer key
 ----------------------------------------------------------------------
-#include <stdio.h>
+#include <assert.h>
 #include <stdlib.h>
 #include "uthash.h"
 
@@ -816,17 +816,16 @@ typedef struct {
 } el_t;
 
 el_t *hash = NULL;
-char *someaddr = NULL;
+void *someaddr = &hash;
 
 int main() {
   el_t *d;
   el_t *e = (el_t *)malloc(sizeof *e);
-  if (!e) return -1;
-  e->key = (void*)someaddr;
+  e->key = someaddr;
   e->i = 1;
   HASH_ADD_PTR(hash, key, e);
   HASH_FIND_PTR(hash, &someaddr, d);
-  if (d) printf("found\n");
+  assert(d == e);
 
   /* release memory */
   HASH_DEL(hash, e);
@@ -835,9 +834,7 @@ int main() {
 }
 ----------------------------------------------------------------------
 
-This example is included in `tests/test57.c`. Note that the end of the program
-deletes the element out of the hash, (and since no more elements remain in the
-hash), uthash releases its internal memory.
+This example is included in `tests/test57.c`.
 
 Structure keys
 ~~~~~~~~~~~~~~
@@ -893,7 +890,7 @@ int main(int argc, char *argv[]) {
 
 ----------------------------------------------------------------------
 
-This usage is nearly the same as use of a compound key explained below.
+This usage is nearly the same as the usage of a compound key explained below.
 
 Note that the general macros require the name of the `UT_hash_handle` to be
 passed as the first argument (here, this is `hh`). The general macros are

tests/test57.ans

@@ -1 +0,0 @@
-found

tests/test57.c

@@ -1,5 +1,5 @@
-#include <stdio.h>
-#include <stdlib.h>
+#include <assert.h>
+#include <stddef.h>
 #include "uthash.h"
 
 typedef struct {
@@ -8,25 +8,46 @@ typedef struct {
     UT_hash_handle hh;
 } el_t;
 
+el_t *findit(el_t *hash, void *keytofind)
+{
+    el_t *found;
+    HASH_FIND_PTR(hash, &keytofind, found);
+    return found;
+}
+
 int main()
 {
-    el_t *d;
     el_t *hash = NULL;
-    char *someaddr = NULL;
-    el_t *e = (el_t*)malloc(sizeof(el_t));
-    if (!e) {
-        return -1;
-    }
-    e->key = (void*)someaddr;
-    e->i = 1;
-    HASH_ADD_PTR(hash,key,e);
-    HASH_FIND_PTR(hash, &someaddr, d);
-    if (d != NULL) {
-        printf("found\n");
-    }
-
-    /* release memory */
-    HASH_DEL(hash,e);
-    free(e);
+    el_t e1;
+    el_t e2;
+
+    e1.key = NULL;
+    e1.i = 1;
+
+    e2.key = &e2;
+    e2.i = 2;
+
+    assert(findit(hash, NULL) == NULL);
+    assert(findit(hash, &e1) == NULL);
+    assert(findit(hash, &e2) == NULL);
+
+    HASH_ADD_PTR(hash, key, &e1);
+    assert(findit(hash, NULL) == &e1);
+    assert(findit(hash, &e1) == NULL);
+    assert(findit(hash, &e2) == NULL);
+
+    HASH_ADD_PTR(hash, key, &e2);
+    assert(findit(hash, NULL) == &e1);
+    assert(findit(hash, &e1) == NULL);
+    assert(findit(hash, &e2) == &e2);
+
+    HASH_DEL(hash, &e1);
+    assert(findit(hash, NULL) == NULL);
+    assert(findit(hash, &e1) == NULL);
+    assert(findit(hash, &e2) == &e2);
+
+    HASH_CLEAR(hh, hash);
+    assert(hash == NULL);
+
     return 0;
 }