fix Except

src/futures/promise_test.cc

@@ -35,3 +35,19 @@ TEST(Future, Basic)
     p.Resolve(1);
     EXPECT_EQ(future.Get(), 21);
 }
+
+TEST(Future, Except)
+{
+    auto p = sled::Promise<int>();
+    p.Resolve(1);
+    p.GetFuture()
+        .Then([](int) { throw std::runtime_error("test"); })
+        .Except([](std::exception_ptr e) {
+            try {
+                std::rethrow_exception(e);
+            } catch (const std::exception &e) {
+                EXPECT_STREQ(e.what(), "test");
+            }
+        })
+        .Get();
+}