add queryability tests for stdexec::env (#1655)

adds tests of the `stdexec::env` utility to check for ability to SFINAE-detect supported and unsupported queries.

Co-authored-by: Eric Niebler <[email protected]>

Author: RobertLeahy

test/CMakeLists.txt

@@ -61,6 +61,7 @@ set(stdexec_test_sources
     stdexec/algos/other/test_execute.cpp
     stdexec/detail/test_completion_signatures.cpp
     stdexec/detail/test_utility.cpp
+    stdexec/queries/test_env.cpp
     stdexec/queries/test_get_forward_progress_guarantee.cpp
     stdexec/queries/test_forwarding_queries.cpp
     )

test/stdexec/queries/test_env.cpp

@@ -0,0 +1,52 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ *                         Copyright (c) 2025 Robert Leahy. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+ * Licensed under the Apache License, Version 2.0 with LLVM Exceptions (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://llvm.org/LICENSE.txt
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <catch2/catch.hpp>
+#include <stdexec/execution.hpp>
+
+namespace {
+
+  template <typename T>
+  concept can_get_domain = requires(const T& t) { t.query(::stdexec::get_domain); };
+
+  namespace zero {
+
+    using env = ::stdexec::env<>;
+    static_assert(std::is_same_v<::stdexec::never_stop_token, ::stdexec::stop_token_of_t<env>>);
+    static_assert(!can_get_domain<env>);
+
+  } // namespace zero
+
+  namespace one {
+    using env = ::stdexec::env<::stdexec::env<>>;
+    static_assert(std::is_same_v<::stdexec::never_stop_token, ::stdexec::stop_token_of_t<env>>);
+    static_assert(!can_get_domain<env>);
+  } // namespace one
+
+  namespace two {
+    using env = ::stdexec::env<::stdexec::env<>, ::stdexec::env<>>;
+    static_assert(std::is_same_v<::stdexec::never_stop_token, ::stdexec::stop_token_of_t<env>>);
+    static_assert(!can_get_domain<env>);
+  } // namespace two
+
+  namespace three {
+    using env = ::stdexec::env<::stdexec::env<>, ::stdexec::env<>, ::stdexec::env<>>;
+    static_assert(std::is_same_v<::stdexec::never_stop_token, ::stdexec::stop_token_of_t<env>>);
+    static_assert(!can_get_domain<env>);
+  } // namespace three
+} // namespace