tests: Add further tests for mpz code.
diff --git a/unix/coverage.c b/unix/coverage.c
index 1f52d9c..d6514b9 100644
--- a/unix/coverage.c
+++ b/unix/coverage.c
@@ -3,6 +3,7 @@
 #include "py/obj.h"
 #include "py/runtime.h"
 #include "py/repl.h"
+#include "py/mpz.h"
 
 #if defined(MICROPY_UNIX_COVERAGE)
 
@@ -83,6 +84,29 @@
         printf("%d\n", MP_OBJ_IS_QSTR(mp_obj_str_intern(mp_obj_new_str("intern me", 9, false))));
     }
 
+    // mpz
+    {
+        printf("# mpz\n");
+
+        mp_uint_t value;
+        mpz_t mpz;
+        mpz_init_zero(&mpz);
+
+        // mpz_as_uint_checked, with success
+        mpz_set_from_int(&mpz, 12345678);
+        printf("%d\n", mpz_as_uint_checked(&mpz, &value));
+        printf("%d\n", (int)value);
+
+        // mpz_as_uint_checked, with negative arg
+        mpz_set_from_int(&mpz, -1);
+        printf("%d\n", mpz_as_uint_checked(&mpz, &value));
+
+        // mpz_as_uint_checked, with overflowing arg
+        mpz_set_from_int(&mpz, 1);
+        mpz_shl_inpl(&mpz, &mpz, 70);
+        printf("%d\n", mpz_as_uint_checked(&mpz, &value));
+    }
+
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_0(extra_coverage_obj, extra_coverage);