tests: kernel: k_heap: add tests for k_heap_realloc

There was zero test for this new-ish kernel API so add them.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

tests/kernel/mem_heap/k_heap_api/src/test_kheap_api.c

@@ -319,3 +319,115 @@ ZTEST(k_heap_api, test_k_heap_array_get)
 	}
 	zassert_true(test_heap_found);
 }
+
+/**
+ * @brief Test k_heap_realloc() API functionality.
+ *
+ * @ingroup k_heap_api_tests
+ *
+ * @details The test validates k_heap_realloc() API by:
+ * 1. Allocating memory and reallocating to a larger size
+ * 2. Reallocating to a smaller size
+ * 3. Verifying data integrity after reallocation
+ *
+ * @see k_heap_realloc()
+ */
+ZTEST(k_heap_api, test_k_heap_realloc)
+{
+	k_timeout_t timeout = Z_TIMEOUT_US(TIMEOUT);
+	char *p, *p2, *p3;
+
+	p = (char *)k_heap_alloc(&k_heap_test, ALLOC_SIZE_1, timeout);
+	zassert_not_null(p, "k_heap_alloc operation failed");
+
+	/* Fill the allocated memory with a pattern */
+	for (int i = 0; i < ALLOC_SIZE_1; i++) {
+		p[i] = 'A' + (i % 26);
+	}
+
+	/* Reallocate to a larger size */
+	p2 = (char *)k_heap_realloc(&k_heap_test, p, ALLOC_SIZE_2, timeout);
+	zassert_not_null(p2, "k_heap_realloc operation failed");
+
+	/* Verify the original data is preserved */
+	for (int i = 0; i < ALLOC_SIZE_1; i++) {
+		zassert_equal(p2[i], 'A' + (i % 26), "Data integrity check failed");
+	}
+
+	/* Reallocate to a smaller size */
+	p3 = (char *)k_heap_realloc(&k_heap_test, p2, ALLOC_SIZE_1 / 2, timeout);
+	zassert_not_null(p3, "k_heap_realloc operation failed");
+
+	/* Verify the data is preserved up to the new size */
+	for (int i = 0; i < ALLOC_SIZE_1 / 2; i++) {
+		zassert_equal(p3[i], 'A' + (i % 26), "Data integrity check failed");
+	}
+
+	k_heap_free(&k_heap_test, p3);
+}
+
+/**
+ * @brief Test k_heap_realloc() with NULL pointer.
+ *
+ * @ingroup k_heap_api_tests
+ *
+ * @details The test validates that k_heap_realloc() behaves like k_heap_alloc()
+ * when called with a NULL pointer.
+ *
+ * @see k_heap_realloc()
+ */
+ZTEST(k_heap_api, test_k_heap_realloc_null)
+{
+	k_timeout_t timeout = Z_TIMEOUT_US(TIMEOUT);
+	char *p = (char *)k_heap_realloc(&k_heap_test, NULL, ALLOC_SIZE_1, timeout);
+
+	zassert_not_null(p, "k_heap_realloc with NULL pointer failed");
+	k_heap_free(&k_heap_test, p);
+}
+
+/**
+ * @brief Test k_heap_realloc() with size 0.
+ *
+ * @ingroup k_heap_api_tests
+ *
+ * @details The test validates that k_heap_realloc() behaves like k_heap_free()
+ * when called with size 0.
+ *
+ * @see k_heap_realloc()
+ */
+ZTEST(k_heap_api, test_k_heap_realloc_zero)
+{
+	char *p, *p2;
+
+	p = (char *)k_heap_alloc(&k_heap_test, ALLOC_SIZE_1, K_NO_WAIT);
+	zassert_not_null(p, "k_heap_alloc operation failed");
+
+	/* Realloc with size 0 should free the memory */
+	p2 = (char *)k_heap_realloc(&k_heap_test, p, 0, K_NO_WAIT);
+	zassert_is_null(p2, "k_heap_realloc with size 0 should return NULL");
+}
+
+/**
+ * @brief Test k_heap_realloc() failure case.
+ *
+ * @ingroup k_heap_api_tests
+ *
+ * @details The test validates that k_heap_realloc() returns NULL when
+ * trying to reallocate to a size larger than the heap.
+ *
+ * @see k_heap_realloc()
+ */
+ZTEST(k_heap_api, test_k_heap_realloc_fail)
+{
+	k_timeout_t timeout = Z_TIMEOUT_US(TIMEOUT);
+	char *p, *p2;
+
+	p = (char *)k_heap_alloc(&k_heap_test, ALLOC_SIZE_1, timeout);
+	zassert_not_null(p, "k_heap_alloc operation failed");
+
+	/* Try to reallocate to a size larger than the heap */
+	p2 = (char *)k_heap_realloc(&k_heap_test, p, HEAP_SIZE + 1, timeout);
+	zassert_is_null(p2, "k_heap_realloc should fail for size larger than heap");
+
+	k_heap_free(&k_heap_test, p);
+}