tests: rename remaining C unit tests to .cpp (no content changes)

tests/test_ref_cpp.cpp

@@ -0,0 +1,63 @@
+#include <assert.h>
+#include <stdlib.h>
+
+#include "ss_ref.h"
+
+typedef struct {
+    ss_ref_t ref;
+    int *destroyed;
+} test_object_t;
+
+static void
+destroy_object(void *object)
+{
+    test_object_t *value = object;
+    ++*value->destroyed;
+    free(value);
+}
+
+static void *
+new_object(int *destroyed)
+{
+    test_object_t *value = malloc(sizeof(*value));
+    assert(value != NULL);
+    ss_ref_init(value, destroy_object);
+    value->destroyed = destroyed;
+    return value;
+}
+
+int
+main(void)
+{
+    int destroyed = 0;
+    void *table = new_object(&destroyed);
+    void *relay = NULL;
+    ss_ref_assign(&relay, table);
+    ss_ref_assign(&relay, relay); /* Self-assignment must preserve ownership. */
+    ss_ptr_reset(&table, ss_ref_release); /* Simulate eviction. */
+    assert(table == NULL && destroyed == 0);
+    ss_ptr_reset(&relay, ss_ref_release);
+    assert(relay == NULL && destroyed == 1);
+    ss_ptr_reset(&relay, ss_ref_release); /* Repeated cleanup is harmless. */
+    assert(destroyed == 1);
+
+    void *query = new_object(&destroyed);
+    relay = new_object(&destroyed);
+    ss_ptr_move(&relay, &query, ss_ref_release);
+    assert(query == NULL && relay != NULL && destroyed == 2);
+    ss_ptr_move(&relay, &relay, ss_ref_release); /* Self-move. */
+    assert(relay != NULL && destroyed == 2);
+    ss_ref_assign(&query, relay);
+    ss_ptr_move(&relay, &query, ss_ref_release); /* Two owners, same object. */
+    assert(query == NULL && relay != NULL && destroyed == 2);
+    ss_ref_assign(&relay, NULL);
+    assert(relay == NULL && destroyed == 3);
+
+    relay = new_object(&destroyed);
+    ss_ptr_move(&relay, &query, ss_ref_release); /* Move an empty source. */
+    assert(relay == NULL && query == NULL && destroyed == 4);
+    assert(ss_ref_retain(NULL) == NULL);
+    ss_ref_release(NULL);
+    ss_ptr_reset(&relay, NULL); /* Legacy crypto has no session/callback. */
+    return 0;
+}