[experiments] A unit test for the experiments framework (#33334)

Adds a test for the experiments codegen. It updates the codegen to parse
test_experiments.yaml and test_experiments_rollouts.yaml files and
generate test_experiments.h and test_experiments.cc files along with an
experiments_test.cc file. The experiments test verifies the returned
value of IsExperimentEnabled with the expected value.

CMakeLists.txt

@@ -968,6 +968,7 @@ if(gRPC_BUILD_TESTS)
   endif()
   add_dependencies(buildtests_cxx exception_test)
   add_dependencies(buildtests_cxx exec_ctx_wakeup_scheduler_test)
+  add_dependencies(buildtests_cxx experiments_test)
   add_dependencies(buildtests_cxx factory_test)
   add_dependencies(buildtests_cxx fake_binder_test)
   add_dependencies(buildtests_cxx fake_resolver_test)
@@ -11403,6 +11404,44 @@ target_link_libraries(exec_ctx_wakeup_scheduler_test
 )
 
 
+endif()
+if(gRPC_BUILD_TESTS)
+
+add_executable(experiments_test
+  test/core/experiments/experiments_test.cc
+  test/core/experiments/fixtures/experiments.cc
+  third_party/googletest/googletest/src/gtest-all.cc
+  third_party/googletest/googlemock/src/gmock-all.cc
+)
+target_compile_features(experiments_test PUBLIC cxx_std_14)
+target_include_directories(experiments_test
+  PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    ${_gRPC_ADDRESS_SORTING_INCLUDE_DIR}
+    ${_gRPC_RE2_INCLUDE_DIR}
+    ${_gRPC_SSL_INCLUDE_DIR}
+    ${_gRPC_UPB_GENERATED_DIR}
+    ${_gRPC_UPB_GRPC_GENERATED_DIR}
+    ${_gRPC_UPB_INCLUDE_DIR}
+    ${_gRPC_XXHASH_INCLUDE_DIR}
+    ${_gRPC_ZLIB_INCLUDE_DIR}
+    third_party/googletest/googletest/include
+    third_party/googletest/googletest
+    third_party/googletest/googlemock/include
+    third_party/googletest/googlemock
+    ${_gRPC_PROTO_GENS_DIR}
+)
+
+target_link_libraries(experiments_test
+  ${_gRPC_BASELIB_LIBRARIES}
+  ${_gRPC_PROTOBUF_LIBRARIES}
+  ${_gRPC_ZLIB_LIBRARIES}
+  ${_gRPC_ALLTARGETS_LIBRARIES}
+  grpc_test_util
+)
+
+
 endif()
 if(gRPC_BUILD_TESTS)
 

build_autogenerated.yaml

@@ -7409,6 +7409,18 @@ targets:
   - gpr
   - upb
   uses_polling: false
+- name: experiments_test
+  gtest: true
+  build: test
+  language: c++
+  headers:
+  - test/core/experiments/fixtures/experiments.h
+  src:
+  - test/core/experiments/experiments_test.cc
+  - test/core/experiments/fixtures/experiments.cc
+  deps:
+  - grpc_test_util
+  uses_polling: false
 - name: factory_test
   gtest: true
   build: test

src/core/BUILD

@@ -126,6 +126,7 @@ grpc_cc_library(
         "absl/strings",
     ],
     language = "c++",
+    tags = ["nofixdeps"],
     deps = [
         "no_destruct",
         "//:config_vars",

src/core/lib/experiments/config.cc

@@ -54,6 +54,31 @@ std::atomic<bool> g_loaded(false);
 absl::AnyInvocable<bool(struct ExperimentMetadata)>* g_check_constraints_cb =
     nullptr;
 
+class TestExperiments {
+ public:
+  TestExperiments(const ExperimentMetadata* experiment_metadata,
+                  size_t num_experiments) {
+    enabled_ = new bool[num_experiments];
+    for (size_t i = 0; i < num_experiments; i++) {
+      if (g_check_constraints_cb != nullptr) {
+        enabled_[i] = (*g_check_constraints_cb)(experiment_metadata[i]);
+      } else {
+        enabled_[i] = experiment_metadata[i].default_value;
+      }
+    }
+  }
+
+  // Overloading [] operator to access elements in array style
+  bool operator[](int index) { return enabled_[index]; }
+
+  ~TestExperiments() { delete enabled_; }
+
+ private:
+  bool* enabled_;
+};
+
+TestExperiments* g_test_experiments = nullptr;
+
 GPR_ATTRIBUTE_NOINLINE Experiments LoadExperimentsFromConfigVariable() {
   g_loaded.store(true, std::memory_order_relaxed);
   // Set defaults from metadata.
@@ -111,11 +136,20 @@ void TestOnlyReloadExperimentsFromConfigVariables() {
   PrintExperimentsList();
 }
 
+void LoadTestOnlyExperimentsFromMetadata(
+    const ExperimentMetadata* experiment_metadata, size_t num_experiments) {
+  g_test_experiments =
+      new TestExperiments(experiment_metadata, num_experiments);
+}
+
 bool IsExperimentEnabled(size_t experiment_id) {
-  // Normal path: just return the value;
   return ExperimentsSingleton().enabled[experiment_id];
 }
 
+bool IsTestExperimentEnabled(size_t experiment_id) {
+  return (*g_test_experiments)[experiment_id];
+}
+
 void PrintExperimentsList() {
   size_t max_experiment_length = 0;
   for (size_t i = 0; i < kNumExperiments; i++) {

src/core/lib/experiments/config.h

@@ -26,17 +26,37 @@
 
 namespace grpc_core {
 
+struct ExperimentMetadata {
+  const char* name;
+  const char* description;
+  const char* additional_constaints;
+  bool default_value;
+  bool allow_in_fuzzing_config;
+};
+
 #ifndef GRPC_EXPERIMENTS_ARE_FINAL
 // Return true if experiment \a experiment_id is enabled.
 // Experiments are numbered by their order in the g_experiment_metadata array
 // declared in experiments.h.
 bool IsExperimentEnabled(size_t experiment_id);
 
+// Given a test experiment id, returns true if the test experiment is enabled.
+// Test experiments can be loaded using the LoadTestOnlyExperimentsFromMetadata
+// method.
+bool IsTestExperimentEnabled(size_t experiment_id);
+
 // Reload experiment state from config variables.
 // Does not change ForceEnableExperiment state.
 // Expects the caller to handle global thread safety - so really only
 // appropriate for carefully written tests.
 void TestOnlyReloadExperimentsFromConfigVariables();
+
+// Reload experiment state from passed metadata.
+// Does not change ForceEnableExperiment state.
+// Expects the caller to handle global thread safety - so really only
+// appropriate for carefully written tests.
+void LoadTestOnlyExperimentsFromMetadata(
+    const ExperimentMetadata* experiment_metadata, size_t num_experiments);
 #endif
 
 // Print out a list of all experiments that are built into this binary.
@@ -49,14 +69,6 @@ void PrintExperimentsList();
 // If this is called twice for the same experiment, both calls must agree.
 void ForceEnableExperiment(absl::string_view experiment_name, bool enable);
 
-struct ExperimentMetadata {
-  const char* name;
-  const char* description;
-  const char* additional_constaints;
-  bool default_value;
-  bool allow_in_fuzzing_config;
-};
-
 // Register a function to be called to validate the value an experiment can
 // take subject to additional constraints.
 // The function will take the ExperimentMetadata as its argument. It will return

test/core/experiments/BUILD

@@ -0,0 +1,47 @@
+# Copyright 2023 gRPC 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.
+
+load("//bazel:grpc_build_system.bzl", "grpc_cc_library", "grpc_cc_test")
+
+grpc_cc_library(
+    name = "experiments_lib",
+    srcs = [
+        "fixtures/experiments.cc",
+    ],
+    hdrs = [
+        "fixtures/experiments.h",
+    ],
+    language = "c++",
+    deps = [
+        "//:config_vars",
+        "//:gpr",
+        "//src/core:experiments",
+        "//src/core:no_destruct",
+    ],
+)
+
+grpc_cc_test(
+    name = "experiments_test",
+    srcs = ["experiments_test.cc"],
+    external_deps = ["gtest"],
+    language = "C++",
+    uses_event_engine = False,
+    uses_polling = False,
+    deps = [
+        ":experiments_lib",
+        "//:gpr",
+        "//src/core:experiments",
+        "//test/core/util:grpc_test_util",
+    ],
+)

test/core/experiments/experiments_test.cc

@@ -0,0 +1,62 @@
+// Copyright 2023 gRPC 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.
+
+// Auto generated by tools/codegen/core/gen_experiments.py
+
+#include <grpc/support/port_platform.h>
+
+#include "test/core/experiments/fixtures/experiments.h"
+
+#include "gtest/gtest.h"
+
+#include "src/core/lib/experiments/config.h"
+
+#ifndef GRPC_EXPERIMENTS_ARE_FINAL
+
+bool GetExperimentTestExperiment1ExpectedValue() { return false; }
+
+bool GetExperimentTestExperiment2ExpectedValue() { return false; }
+
+bool GetExperimentTestExperiment3ExpectedValue() {
+#ifdef NDEBUG
+  return false;
+#else
+  return true;
+#endif
+}
+
+bool GetExperimentTestExperiment4ExpectedValue() { return true; }
+
+TEST(ExperimentsTest, CheckExperimentValuesTest) {
+  ASSERT_EQ(grpc_core::IsTestExperiment1Enabled(),
+            GetExperimentTestExperiment1ExpectedValue());
+
+  ASSERT_EQ(grpc_core::IsTestExperiment2Enabled(),
+            GetExperimentTestExperiment2ExpectedValue());
+
+  ASSERT_EQ(grpc_core::IsTestExperiment3Enabled(),
+            GetExperimentTestExperiment3ExpectedValue());
+
+  ASSERT_EQ(grpc_core::IsTestExperiment4Enabled(),
+            GetExperimentTestExperiment4ExpectedValue());
+}
+
+#endif  // GRPC_EXPERIMENTS_ARE_FINAL
+
+int main(int argc, char** argv) {
+  testing::InitGoogleTest(&argc, argv);
+  grpc_core::LoadTestOnlyExperimentsFromMetadata(
+      grpc_core::g_test_experiment_metadata, grpc_core::kNumTestExperiments);
+  return RUN_ALL_TESTS();
+}

test/core/experiments/fixtures/experiments.cc

@@ -0,0 +1,52 @@
+// Copyright 2023 gRPC 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.
+
+// Auto generated by tools/codegen/core/gen_experiments.py
+
+#include <grpc/support/port_platform.h>
+
+#include "test/core/experiments/fixtures/experiments.h"
+
+#ifndef GRPC_EXPERIMENTS_ARE_FINAL
+namespace {
+const char* const description_test_experiment_1 = "Test Experiment 1";
+const char* const additional_constraints_test_experiment_1 = "{}";
+const char* const description_test_experiment_2 = "Test Experiment 2";
+const char* const additional_constraints_test_experiment_2 = "{}";
+const char* const description_test_experiment_3 = "Test Experiment 3";
+const char* const additional_constraints_test_experiment_3 = "{}";
+const char* const description_test_experiment_4 = "Test Experiment 4";
+const char* const additional_constraints_test_experiment_4 = "{}";
+#ifdef NDEBUG
+const bool kDefaultForDebugOnly = false;
+#else
+const bool kDefaultForDebugOnly = true;
+#endif
+}  // namespace
+
+namespace grpc_core {
+
+const ExperimentMetadata g_test_experiment_metadata[] = {
+    {"test_experiment_1", description_test_experiment_1,
+     additional_constraints_test_experiment_1, false, true},
+    {"test_experiment_2", description_test_experiment_2,
+     additional_constraints_test_experiment_2, false, true},
+    {"test_experiment_3", description_test_experiment_3,
+     additional_constraints_test_experiment_3, kDefaultForDebugOnly, true},
+    {"test_experiment_4", description_test_experiment_4,
+     additional_constraints_test_experiment_4, true, true},
+};
+
+}  // namespace grpc_core
+#endif

test/core/experiments/fixtures/experiments.h

@@ -0,0 +1,90 @@
+// Copyright 2023 gRPC 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.
+
+// Auto generated by tools/codegen/core/gen_experiments.py
+//
+// This file contains the autogenerated parts of the experiments API.
+//
+// It generates two symbols for each experiment.
+//
+// For the experiment named new_car_project, it generates:
+//
+// - a function IsNewCarProjectEnabled() that returns true if the experiment
+//   should be enabled at runtime.
+//
+// - a macro GRPC_EXPERIMENT_IS_INCLUDED_NEW_CAR_PROJECT that is defined if the
+//   experiment *could* be enabled at runtime.
+//
+// The function is used to determine whether to run the experiment or
+// non-experiment code path.
+//
+// If the experiment brings significant bloat, the macro can be used to avoid
+// including the experiment code path in the binary for binaries that are size
+// sensitive.
+//
+// By default that includes our iOS and Android builds.
+//
+// Finally, a small array is included that contains the metadata for each
+// experiment.
+//
+// A macro, GRPC_EXPERIMENTS_ARE_FINAL, controls whether we fix experiment
+// configuration at build time (if it's defined) or allow it to be tuned at
+// runtime (if it's disabled).
+//
+// If you are using the Bazel build system, that macro can be configured with
+// --define=grpc_experiments_are_final=true
+
+#ifndef GRPC_TEST_CORE_EXPERIMENTS_FIXTURES_EXPERIMENTS_H
+#define GRPC_TEST_CORE_EXPERIMENTS_FIXTURES_EXPERIMENTS_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stddef.h>
+
+#include "src/core/lib/experiments/config.h"
+
+namespace grpc_core {
+
+#ifdef GRPC_EXPERIMENTS_ARE_FINAL
+inline bool IsTestExperiment1Enabled() { return false; }
+inline bool IsTestExperiment2Enabled() { return false; }
+#ifndef NDEBUG
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_3
+#endif
+inline bool IsTestExperiment3Enabled() {
+#ifdef NDEBUG
+  return false;
+#else
+  return true;
+#endif
+}
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_4
+inline bool IsTestExperiment4Enabled() { return true; }
+#else
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_1
+inline bool IsTestExperiment1Enabled() { return IsTestExperimentEnabled(0); }
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_2
+inline bool IsTestExperiment2Enabled() { return IsTestExperimentEnabled(1); }
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_3
+inline bool IsTestExperiment3Enabled() { return IsTestExperimentEnabled(2); }
+#define GRPC_EXPERIMENT_IS_INCLUDED_TEST_EXPERIMENT_4
+inline bool IsTestExperiment4Enabled() { return IsTestExperimentEnabled(3); }
+
+constexpr const size_t kNumTestExperiments = 4;
+extern const ExperimentMetadata g_test_experiment_metadata[kNumTestExperiments];
+
+#endif
+}  // namespace grpc_core
+
+#endif  // GRPC_TEST_CORE_EXPERIMENTS_FIXTURES_EXPERIMENTS_H

test/core/experiments/fixtures/test_experiments.yaml

@@ -0,0 +1,30 @@
+# Copyright 2023 gRPC 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.
+
+- name: test_experiment_1
+  description: Test Experiment 1
+  expiry: 2023/08/01
+  owner: blah@abc.com
+- name: test_experiment_2
+  description: Test Experiment 2
+  expiry: 2023/01/01
+  owner: blah1@abc.com
+- name: test_experiment_3
+  description: Test Experiment 3
+  expiry: 2024/01/01
+  owner: blah2@abc.com
+- name: test_experiment_4
+  description: Test Experiment 4
+  expiry: 2022/01/01
+  owner: blah3@abc.com

test/core/experiments/fixtures/test_experiments_rollout.yaml

@@ -0,0 +1,22 @@
+# Copyright 2023 gRPC 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.
+
+- name: test_experiment_1
+  default: broken
+- name: test_experiment_2
+  default: false
+- name: test_experiment_3
+  default: debug
+- name: test_experiment_4
+  default: true

tools/codegen/core/experiments_compiler.py

@@ -64,7 +64,48 @@ If you are using the Bazel build system, that macro can be configured with
 """
 
 
-def ToCStr(s, encoding="ascii"):
+def _EXPERIMENTS_TEST_SKELETON(defs, test_body):
+    return f"""
+#include <grpc/support/port_platform.h>
+
+#include "test/core/experiments/fixtures/experiments.h"
+#include "gtest/gtest.h"
+
+#include "src/core/lib/experiments/config.h"
+
+#ifndef GRPC_EXPERIMENTS_ARE_FINAL
+{defs}
+TEST(ExperimentsTest, CheckExperimentValuesTest) {{
+{test_body}
+}}
+
+#endif // GRPC_EXPERIMENTS_ARE_FINAL
+
+int main(int argc, char** argv) {{
+  testing::InitGoogleTest(&argc, argv);
+  grpc_core::LoadTestOnlyExperimentsFromMetadata(
+    grpc_core::g_test_experiment_metadata, grpc_core::kNumTestExperiments);
+  return RUN_ALL_TESTS();
+}}
+"""
+
+
+def _EXPERIMENTS_EXPECTED_VALUE(name, expected_value):
+    return f"""
+bool GetExperiment{name}ExpectedValue() {{
+{expected_value}
+}}
+"""
+
+
+def _EXPERIMENT_CHECK_TEXT(name):
+    return f"""
+  ASSERT_EQ(grpc_core::Is{name}Enabled(),
+            GetExperiment{name}ExpectedValue());
+"""
+
+
+def ToCStr(s, encoding='ascii'):
     if isinstance(s, str):
         s = s.encode(encoding)
     result = ""
@@ -268,7 +309,7 @@ class ExperimentsCompiler(object):
             rollout_attributes["name"]
         ].AddRolloutSpecification(self._defaults, rollout_attributes)
 
-    def GenerateExperimentsHdr(self, output_file):
+    def GenerateExperimentsHdr(self, output_file, mode):
         with open(output_file, "w") as H:
             PutCopyright(H, "//")
             PutBanner(
@@ -278,8 +319,18 @@ class ExperimentsCompiler(object):
                 "//",
             )
 
-            print("#ifndef GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
-            print("#define GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
+            if mode != "test":
+                include_guard = "GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H"
+            else:
+                file_path_list = output_file.split("/")[0:-1]
+                file_name = output_file.split("/")[-1].split(".")[0]
+
+                include_guard = (
+                    f"GRPC_{'_'.join(path.upper() for path in file_path_list)}_{file_name.upper()}_H"
+                )
+
+            print(f"#ifndef {include_guard}", file=H)
+            print(f"#define {include_guard}", file=H)
             print(file=H)
             print("#include <grpc/support/port_platform.h>", file=H)
             print(file=H)
@@ -313,20 +364,27 @@ class ExperimentsCompiler(object):
                 )
                 print(
                     "inline bool Is%sEnabled() { return"
-                    " IsExperimentEnabled(%d); }"
-                    % (SnakeToPascal(exp.name), i),
+                    " Is%sExperimentEnabled(%d); }"
+                    % (SnakeToPascal(exp.name), "Test" if mode == "test" else "", i),
                     file=H,
                 )
             print(file=H)
+
+            if mode == "test":
+                num_experiments_var_name = "kNumTestExperiments"
+                experiments_metadata_var_name = "g_test_experiment_metadata"
+            else:
+                num_experiments_var_name = "kNumExperiments"
+                experiments_metadata_var_name = "g_experiment_metadata"
             print(
-                "constexpr const size_t kNumExperiments = %d;"
-                % len(self._experiment_definitions.keys()),
+                f"constexpr const size_t {num_experiments_var_name} = "
+                f"{len(self._experiment_definitions.keys())};",
                 file=H,
             )
             print(
                 (
                     "extern const ExperimentMetadata"
-                    " g_experiment_metadata[kNumExperiments];"
+                    f" {experiments_metadata_var_name}[{num_experiments_var_name}];"
                 ),
                 file=H,
             )
@@ -334,11 +392,9 @@ class ExperimentsCompiler(object):
             print("#endif", file=H)
             print("}  // namespace grpc_core", file=H)
             print(file=H)
-            print(
-                "#endif  // GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H
-            )
+            print(f"#endif  // {include_guard}", file=H)
 
-    def GenerateExperimentsSrc(self, output_file):
+    def GenerateExperimentsSrc(self, output_file, header_file_path, mode):
         with open(output_file, "w") as C:
             PutCopyright(C, "//")
             PutBanner(
@@ -348,7 +404,7 @@ class ExperimentsCompiler(object):
             )
 
             print("#include <grpc/support/port_platform.h>", file=C)
-            print('#include "src/core/lib/experiments/experiments.h"', file=C)
+            print(f"#include \"{header_file_path}\"", file=C)
             print(file=C)
             print("#ifndef GRPC_EXPERIMENTS_ARE_FINAL", file=C)
             print("namespace {", file=C)
@@ -380,8 +436,12 @@ class ExperimentsCompiler(object):
             print(file=C)
             print("namespace grpc_core {", file=C)
             print(file=C)
+            if mode == "test":
+                experiments_metadata_var_name = "g_test_experiment_metadata"
+            else:
+                experiments_metadata_var_name = "g_experiment_metadata"
             print(
-                "const ExperimentMetadata g_experiment_metadata[] = {", file=C
+                f"const ExperimentMetadata {experiments_metadata_var_name}[] = {{", file=C
             )
             for _, exp in self._experiment_definitions.items():
                 print(
@@ -400,6 +460,21 @@ class ExperimentsCompiler(object):
             print("}  // namespace grpc_core", file=C)
             print("#endif", file=C)
 
+    def GenTest(self, output_file):
+        with open(output_file, 'w') as C:
+            PutCopyright(C, "//")
+            PutBanner(
+                [C],
+                ["Auto generated by tools/codegen/core/gen_experiments.py"],
+                "//")
+            defs = ""
+            test_body = ""
+            for _, exp in self._experiment_definitions.items():
+                defs += _EXPERIMENTS_EXPECTED_VALUE(
+                    SnakeToPascal(exp.name), self._final_return[exp.default])
+                test_body += _EXPERIMENT_CHECK_TEXT(SnakeToPascal(exp.name))
+            print(_EXPERIMENTS_TEST_SKELETON(defs, test_body), file=C)
+
     def GenExperimentsBzl(self, output_file):
         if self._bzl_list_for_defaults is None:
             return

tools/codegen/core/gen_experiments.py

@@ -74,63 +74,69 @@ def ParseCommandLineArguments(args):
         action="store_false",
         help="If specified, disables checking experiment expiry dates",
     )
-    flag_parser.add_argument(
-        "--disable_gen_hdrs",
-        action="store_true",
-        help="If specified, disables generation of experiments hdr files",
-    )
-    flag_parser.add_argument(
-        "--disable_gen_srcs",
-        action="store_true",
-        help="If specified, disables generation of experiments source files",
-    )
-    flag_parser.add_argument(
-        "--disable_gen_bzl",
-        action="store_true",
-        help="If specified, disables generation of experiments.bzl file",
-    )
     return flag_parser.parse_args(args)
 
 
 args = ParseCommandLineArguments(sys.argv[1:])
 
-with open("src/core/lib/experiments/experiments.yaml") as f:
-    attrs = yaml.safe_load(f.read())
 
-with open("src/core/lib/experiments/rollouts.yaml") as f:
-    rollouts = yaml.safe_load(f.read())
+def _GenerateExperimentFiles(args, mode):
+    if mode == "test":
+        _EXPERIMENTS_DEFS = "test/core/experiments/fixtures/test_experiments.yaml"
+        _EXPERIMENTS_ROLLOUTS = (
+            "test/core/experiments/fixtures/test_experiments_rollout.yaml"
+        )
+        _EXPERIMENTS_HDR_FILE = "test/core/experiments/fixtures/experiments.h"
+        _EXPERIMENTS_SRC_FILE = "test/core/experiments/fixtures/experiments.cc"
+    else:
+        _EXPERIMENTS_DEFS = "src/core/lib/experiments/experiments.yaml"
+        _EXPERIMENTS_ROLLOUTS = "src/core/lib/experiments/rollouts.yaml"
+        _EXPERIMENTS_HDR_FILE = "src/core/lib/experiments/experiments.h"
+        _EXPERIMENTS_SRC_FILE = "src/core/lib/experiments/experiments.cc"
 
-compiler = exp.ExperimentsCompiler(
-    DEFAULTS, FINAL_RETURN, FINAL_DEFINE, BZL_LIST_FOR_DEFAULTS
-)
+    with open(_EXPERIMENTS_DEFS) as f:
+        attrs = yaml.safe_load(f.read())
 
-experiment_annotation = "gRPC Experiments: "
-for attr in attrs:
-    exp_definition = exp.ExperimentDefinition(attr)
-    if not exp_definition.IsValid(args.check):
-        sys.exit(1)
-    experiment_annotation += exp_definition.name + ":0,"
-    if not compiler.AddExperimentDefinition(exp_definition):
-        print("Experiment = %s ERROR adding" % exp_definition.name)
+    with open(_EXPERIMENTS_ROLLOUTS) as f:
+        rollouts = yaml.safe_load(f.read())
+
+    compiler = exp.ExperimentsCompiler(
+        DEFAULTS, FINAL_RETURN, FINAL_DEFINE, BZL_LIST_FOR_DEFAULTS
+    )
+
+    experiment_annotation = "gRPC Experiments: "
+    for attr in attrs:
+        exp_definition = exp.ExperimentDefinition(attr)
+        if not exp_definition.IsValid(args.check):
+            sys.exit(1)
+        experiment_annotation += exp_definition.name + ":0,"
+        if not compiler.AddExperimentDefinition(exp_definition):
+            print("Experiment = %s ERROR adding" % exp_definition.name)
+            sys.exit(1)
+
+    if len(experiment_annotation) > 2000:
+        print("comma-delimited string of experiments is too long")
         sys.exit(1)
 
-if len(experiment_annotation) > 2000:
-    print("comma-delimited string of experiments is too long")
-    sys.exit(1)
+    for rollout_attr in rollouts:
+        if not compiler.AddRolloutSpecification(rollout_attr):
+            print("ERROR adding rollout spec")
+            sys.exit(1)
 
-for rollout_attr in rollouts:
-    if not compiler.AddRolloutSpecification(rollout_attr):
-        print("ERROR adding rollout spec")
-        sys.exit(1)
+    print(f"Mode = {mode} Generating experiments headers")
+    compiler.GenerateExperimentsHdr(_EXPERIMENTS_HDR_FILE, mode)
+  
+    print(f"Mode = {mode} Generating experiments srcs")
+    compiler.GenerateExperimentsSrc(
+        _EXPERIMENTS_SRC_FILE, _EXPERIMENTS_HDR_FILE, mode)
 
-if not args.disable_gen_hdrs:
-    print("Generating experiments headers")
-    compiler.GenerateExperimentsHdr("src/core/lib/experiments/experiments.h")
+    if mode == "test":
+        print("Generating experiments tests")
+        compiler.GenTest('test/core/experiments/experiments_test.cc')
+    else:
+        print("Generating experiments.bzl")
+        compiler.GenExperimentsBzl("bazel/experiments.bzl")
 
-if not args.disable_gen_srcs:
-    print("Generating experiments srcs")
-    compiler.GenerateExperimentsSrc("src/core/lib/experiments/experiments.cc")
 
-if not args.disable_gen_bzl:
-    print("Generating experiments.bzl")
-    compiler.GenExperimentsBzl("bazel/experiments.bzl")
+_GenerateExperimentFiles(args, "production")
+_GenerateExperimentFiles(args, "test")

tools/distrib/fix_build_deps.py

@@ -160,6 +160,7 @@ INTERNAL_DEPS = {
         "//test/core/event_engine/fuzzing_event_engine"
     ),
     "test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.pb.h": "//test/core/event_engine/fuzzing_event_engine:fuzzing_event_engine_proto",
+    "test/core/experiments/test_experiments.h": "//test/core/experiments:test_experiments_lib",
     "google/api/expr/v1alpha1/syntax.upb.h": "google_type_expr_upb",
     "google/rpc/status.upb.h": "google_rpc_status_upb",
     "google/protobuf/any.upb.h": "protobuf_any_upb",

tools/run_tests/generated/tests.json

@@ -3179,6 +3179,30 @@
     ],
     "uses_polling": false
   },
+  {
+    "args": [],
+    "benchmark": false,
+    "ci_platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "cpu_cost": 1.0,
+    "exclude_configs": [],
+    "exclude_iomgrs": [],
+    "flaky": false,
+    "gtest": true,
+    "language": "c++",
+    "name": "experiments_test",
+    "platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "uses_polling": false
+  },
   {
     "args": [],
     "benchmark": false,