diff --git a/tests/unit/expansion/expand.c b/tests/unit/expansion/expand.c
index cb84c80..fd4295d 100644
--- a/tests/unit/expansion/expand.c
+++ b/tests/unit/expansion/expand.c
@@ -3,6 +3,7 @@
 #include <criterion/new/assert.h>
 #include <criterion/redirect.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "../../../src/expansion/expansion.h"
 #include "../../../src/utils/ast/ast.h"
@@ -234,3 +235,43 @@ Test(expand, random)
               "RANDOM variable should expand to a value between 0 and 32767");
     ast_free(&ast);
 }
+
+Test(expand, pid)
+{
+    char str[] = "$$";
+    char *str_heap = strdup(str);
+    struct list *list = list_append(NULL, str_heap);
+    struct ast *ast = ast_create_command(list);
+    struct ast_command *ast_command = ast_get_command(ast);
+
+    struct hash_map *vars = vars_init();
+    vars_default(vars);
+
+    struct ast_command *command2 = expand(ast_command, vars);
+    cr_assert_not_null(command2, "Expansion returned NULL");
+    int pid = atoi((char *)command2->command->data);
+    cr_assert(pid == getpid(),
+              "$$ variable should expand to the pid of the process");
+    ast_free(&ast);
+    hash_map_free(&vars);
+}
+
+Test(expand, default_last_exit_code)
+{
+    char str[] = "$?";
+    char *str_heap = strdup(str);
+    struct list *list = list_append(NULL, str_heap);
+    struct ast *ast = ast_create_command(list);
+    struct ast_command *ast_command = ast_get_command(ast);
+
+    struct hash_map *vars = vars_init();
+    vars_default(vars);
+
+    struct ast_command *command2 = expand(ast_command, vars);
+    cr_assert_not_null(command2, "Expansion returned NULL");
+    int code = atoi((char *)command2->command->data);
+    cr_assert(code == 0,
+              "$? variable should expand to the last exit code (default 0)");
+    ast_free(&ast);
+    hash_map_free(&vars);
+}