[core] Add cpp test for array.h (#49369)

The test is all compile time and static_assert.

---------

Signed-off-by: Ruiyang Wang <[email protected]>

src/ray/util/tests/BUILD

@@ -1,6 +1,17 @@
 load("@rules_cc//cc:defs.bzl", "cc_test")
 load("//bazel:ray.bzl", "COPTS")
 
+cc_test(
+    name = "array_test",
+    srcs = ["array_test.cc"],
+    copts = COPTS,
+    tags = ["team:core"],
+    deps = [
+        "//src/ray/util",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "thread_checker_test",
     srcs = ["thread_checker_test.cc"],

src/ray/util/tests/array_test.cc

@@ -0,0 +1,47 @@
+// Copyright 2024 The Ray Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+// 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 "ray/util/array.h"
+
+#include <gtest/gtest.h>
+
+// Tests for array.h
+// All tests are compile time tests with static_assert, because they are intended to be
+// used in compile time code.
+
+namespace ray {
+
+// Unique array tests
+static constexpr bool array_unique_true = ArrayIsUnique(std::array<int, 3>{1, 2, 3});
+static constexpr bool array_unique_false = ArrayIsUnique(std::array<int, 3>{1, 2, 2});
+
+static_assert(array_unique_true, "Array should have unique elements");
+static_assert(!array_unique_false, "Array should not have unique elements");
+
+// String view unique tests
+static constexpr bool array_unique_sv_true =
+    ArrayIsUnique(std::array<std::string_view, 3>{"a", "b", "c"});
+static constexpr bool array_unique_sv_false =
+    ArrayIsUnique(std::array<std::string_view, 3>{"a", "b", "b"});
+
+static_assert(array_unique_sv_true, "String view array should have unique elements");
+static_assert(!array_unique_sv_false,
+              "String view array should not have unique elements");
+
+static constexpr bool index_of_int = IndexOf(std::array<int, 3>{1, 2, 3}, 2) == 1;
+static_assert(index_of_int, "Index of int should be 1");
+
+// can't test IndexOf not found because it's a compile error
+
+}  // namespace ray