Add tests for moving and swapping promises.

common/BUILD

@@ -95,6 +95,7 @@ cc_test(
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/status:status_matchers",
         "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/synchronization",
         "@com_google_absl//absl/time",
         "@com_google_googletest//:gtest_main",
     ],

common/promise_test.cc

@@ -1,10 +1,12 @@
 #include "common/promise.h"
 
 #include <string>
+#include <utility>
 
 #include "absl/status/status.h"
 #include "absl/status/status_matchers.h"
 #include "absl/status/statusor.h"
+#include "absl/synchronization/notification.h"
 #include "absl/time/time.h"
 #include "common/mock_clock.h"
 #include "common/scheduler.h"
@@ -1411,4 +1413,33 @@ TEST_F(PromiseTest, RejectVoid) {
   EXPECT_TRUE(done);
 }
 
+TEST_F(PromiseTest, MoveConstruct) {
+  auto p1 = Promise<int>::Resolve(42);
+  Promise<int> p2{std::move(p1)};
+  std::move(p2).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(42)); });
+}
+
+TEST_F(PromiseTest, MoveAssign) {
+  auto p1 = Promise<int>::Resolve(42);
+  Promise<int> p2;
+  p2 = std::move(p1);
+  std::move(p2).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(42)); });
+}
+
+TEST_F(PromiseTest, Swap) {
+  auto p1 = Promise<int>::Resolve(42);
+  auto p2 = Promise<int>::Resolve(43);
+  p1.swap(p2);
+  std::move(p1).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(43)); });
+  std::move(p2).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(42)); });
+}
+
+TEST_F(PromiseTest, AdlSwap) {
+  auto p1 = Promise<int>::Resolve(42);
+  auto p2 = Promise<int>::Resolve(43);
+  swap(p1, p2);
+  std::move(p1).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(43)); });
+  std::move(p2).Then([](absl::StatusOr<int> const value) { EXPECT_THAT(value, IsOkAndHolds(42)); });
+}
+
 }  // namespace