It was for my own consumption, sorry opened by mistake

CMakeLists.txt

@@ -10,103 +10,108 @@ include_directories(src/include)
 include_directories(third_party/substrait)
 include_directories(third_party/)
 
+# refer source by absolute path. So that we can use the same source in the child profile too (i.e. test/c)
+set(THIRD_PARTY_DIR "${CMAKE_CURRENT_SOURCE_DIR}/third_party")
 set(PROTOBUF_SOURCES
-    third_party/google/protobuf/any.cc
-    third_party/google/protobuf/any.pb.cc
-    third_party/google/protobuf/any_lite.cc
-    third_party/google/protobuf/arena.cc
-    third_party/google/protobuf/arenastring.cc
-    third_party/google/protobuf/descriptor.cc
-    third_party/google/protobuf/descriptor.pb.cc
-    third_party/google/protobuf/descriptor_database.cc
-    third_party/google/protobuf/dynamic_message.cc
-    third_party/google/protobuf/empty.pb.cc
-    third_party/google/protobuf/extension_set.cc
-    third_party/google/protobuf/extension_set_heavy.cc
-    third_party/google/protobuf/generated_enum_util.cc
-    third_party/google/protobuf/generated_message_bases.cc
-    third_party/google/protobuf/generated_message_reflection.cc
-    third_party/google/protobuf/generated_message_table_driven.cc
-    third_party/google/protobuf/generated_message_table_driven_lite.cc
-    third_party/google/protobuf/generated_message_util.cc
-    third_party/google/protobuf/implicit_weak_message.cc
-    third_party/google/protobuf/inlined_string_field.cc
-    third_party/google/protobuf/map.cc
-    third_party/google/protobuf/map_field.cc
-    third_party/google/protobuf/message.cc
-    third_party/google/protobuf/message_lite.cc
-    third_party/google/protobuf/parse_context.cc
-    third_party/google/protobuf/port_def.inc
-    third_party/google/protobuf/port_undef.inc
-    third_party/google/protobuf/reflection_ops.cc
-    third_party/google/protobuf/repeated_field.cc
-    third_party/google/protobuf/repeated_ptr_field.cc
-    third_party/google/protobuf/text_format.cc
-    third_party/google/protobuf/unknown_field_set.cc
-    third_party/google/protobuf/wire_format.cc
-    third_party/google/protobuf/wire_format_lite.cc
-    third_party/google/protobuf/io/coded_stream.cc
-    third_party/google/protobuf/io/io_win32.cc
-    third_party/google/protobuf/io/strtod.cc
-    third_party/google/protobuf/io/tokenizer.cc
-    third_party/google/protobuf/io/zero_copy_stream.cc
-    third_party/google/protobuf/io/zero_copy_stream_impl.cc
-    third_party/google/protobuf/io/zero_copy_stream_impl_lite.cc
-    third_party/google/protobuf/stubs/common.cc
-    third_party/google/protobuf/stubs/int128.cc
-    third_party/google/protobuf/stubs/status.cc
-    third_party/google/protobuf/stubs/stringpiece.cc
-    third_party/google/protobuf/stubs/stringprintf.cc
-    third_party/google/protobuf/stubs/structurally_valid.cc
-    third_party/google/protobuf/stubs/strutil.cc
-    third_party/google/protobuf/stubs/substitute.cc
-    third_party/google/protobuf/stubs/bytestream.cc
-    third_party/google/protobuf/util/json_util.cc
-    third_party/google/protobuf/util/internal/datapiece.cc
-    third_party/google/protobuf/util/internal/default_value_objectwriter.cc
-    third_party/google/protobuf/util/internal/error_listener.cc
-    third_party/google/protobuf/util/internal/json_escaping.cc
-    third_party/google/protobuf/util/internal/json_objectwriter.cc
-    third_party/google/protobuf/util/internal/json_stream_parser.cc
-    third_party/google/protobuf/util/json_util.cc
-    third_party/google/protobuf/util/internal/object_writer.cc
-    third_party/google/protobuf/util/internal/proto_writer.cc
-    third_party/google/protobuf/util/internal/protostream_objectsource.cc
-    third_party/google/protobuf/util/internal/protostream_objectwriter.cc
-    third_party/google/protobuf/source_context.pb.cc
-    third_party/google/protobuf/stubs/statusor.cc
-    third_party/google/protobuf/stubs/time.cc
-    third_party/google/protobuf/type.pb.cc
-    third_party/google/protobuf/wrappers.pb.cc
-    third_party/google/protobuf/struct.pb.cc
-    third_party/google/protobuf/util/internal/type_info.cc
-    third_party/google/protobuf/util/internal/field_mask_utility.cc
-    third_party/google/protobuf/util/type_resolver_util.cc
-    third_party/google/protobuf/util/internal/utility.cc)
+    ${THIRD_PARTY_DIR}/google/protobuf/any.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/any.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/any_lite.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/arena.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/arenastring.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/descriptor.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/descriptor.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/descriptor_database.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/dynamic_message.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/empty.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/extension_set.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/extension_set_heavy.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_enum_util.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_message_bases.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_message_reflection.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_message_table_driven.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_message_table_driven_lite.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/generated_message_util.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/implicit_weak_message.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/inlined_string_field.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/map.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/map_field.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/message.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/message_lite.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/parse_context.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/port_def.inc
+    ${THIRD_PARTY_DIR}/google/protobuf/port_undef.inc
+    ${THIRD_PARTY_DIR}/google/protobuf/reflection_ops.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/repeated_field.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/repeated_ptr_field.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/text_format.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/unknown_field_set.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/wire_format.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/wire_format_lite.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/coded_stream.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/io_win32.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/strtod.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/tokenizer.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/zero_copy_stream.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/zero_copy_stream_impl.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/io/zero_copy_stream_impl_lite.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/common.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/int128.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/status.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/stringpiece.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/stringprintf.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/structurally_valid.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/strutil.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/substitute.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/bytestream.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/json_util.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/datapiece.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/default_value_objectwriter.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/error_listener.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/json_escaping.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/json_objectwriter.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/json_stream_parser.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/json_util.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/object_writer.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/proto_writer.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/protostream_objectsource.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/protostream_objectwriter.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/source_context.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/statusor.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/stubs/time.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/type.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/wrappers.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/struct.pb.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/type_info.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/field_mask_utility.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/type_resolver_util.cc
+    ${THIRD_PARTY_DIR}/google/protobuf/util/internal/utility.cc)
 
 set(SUBSTRAIT_SOURCES
-    third_party/substrait/substrait/algebra.pb.cc
-    third_party/substrait/substrait/capabilities.pb.cc
-    third_party/substrait/substrait/function.pb.cc
-    third_party/substrait/substrait/parameterized_types.pb.cc
-    third_party/substrait/substrait/plan.pb.cc
-    third_party/substrait/substrait/type.pb.cc
-    third_party/substrait/substrait/type_expressions.pb.cc
-    third_party/substrait/substrait/extensions/extensions.pb.cc)
+    ${THIRD_PARTY_DIR}/substrait/substrait/algebra.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/capabilities.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/function.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/parameterized_types.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/plan.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/type.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/type_expressions.pb.cc
+    ${THIRD_PARTY_DIR}/substrait/substrait/extensions/extensions.pb.cc)
 
+# refer source by absolute path. So that we can use the same source in the child profile too (i.e. test/c)
+set(EXTENSION_SOURCES_DIR "${CMAKE_CURRENT_SOURCE_DIR}/src")
 set(EXTENSION_SOURCES
-    src/to_substrait.cpp
-    src/from_substrait.cpp
-    src/substrait_extension.cpp
-    src/custom_extensions.cpp
-    src/custom_extensions_generated.cpp
+    ${EXTENSION_SOURCES_DIR}/to_substrait.cpp
+    ${EXTENSION_SOURCES_DIR}/from_substrait.cpp
+    ${EXTENSION_SOURCES_DIR}/substrait_extension.cpp
+    ${EXTENSION_SOURCES_DIR}/custom_extensions.cpp
+    ${EXTENSION_SOURCES_DIR}/custom_extensions_generated.cpp
     ${SUBSTRAIT_SOURCES}
     ${PROTOBUF_SOURCES})
 
 add_library(${EXTENSION_NAME} STATIC ${EXTENSION_SOURCES})
 
 set(PARAMETERS "-warnings")
 build_loadable_extension(${TARGET_NAME} ${PARAMETERS} ${EXTENSION_SOURCES})
+add_subdirectory(test/c)
 
 install(
   TARGETS ${EXTENSION_NAME}

extension_config.cmake

@@ -5,4 +5,5 @@ duckdb_extension_load(substrait
     SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR}
     INCLUDE_DIR ${CMAKE_CURRENT_LIST_DIR}/src/include
     LOAD_TESTS
+    DONT_LINK
 )

test/c/CMakeLists.txt

@@ -12,10 +12,15 @@ include_directories(../../duckdb/src/include)
 include_directories(../../duckdb/test/include)
 include_directories(../../duckdb/third_party/catch)
 
-set(ALL_SOURCES test_substrait_c_api.cpp)
+# get all source files from test/helpers
+file(GLOB TEST_HELPER_SOURCES "../../duckdb/test/helpers/*.cpp")
+set(ALL_SOURCES ${EXTENSION_SOURCES} ${TEST_HELPER_SOURCES} test_substrait_c_api.cpp)
 
+# this add_executable is needed to make unit test a target
+add_executable(test_substrait test_substrait_c_api.cpp ${ALL_SOURCES})
+# add duckdb static library to the test so that duckdb symbols are available
+target_link_libraries(test_substrait duckdb_static)
 
-add_library_unity(test_substrait OBJECT ${ALL_SOURCES})
 set(ALL_OBJECT_FILES
     ${ALL_OBJECT_FILES} $<TARGET_OBJECTS:test_substrait>
     PARENT_SCOPE)

test/c/test_substrait_c_api.cpp

@@ -1,19 +1,22 @@
+#define CATCH_CONFIG_RUNNER
 #include "catch.hpp"
 #include "test_helpers.hpp"
-#include "duckdb/parser/parser.hpp"
-#include "duckdb/planner/logical_operator.hpp"
 #include "duckdb/main/connection_manager.hpp"
 #include "substrait_extension.hpp"
 
-#include <chrono>
-#include <thread>
 
 using namespace duckdb;
 using namespace std;
 
+int main(int argc, char* argv[]) {
+    // Call Catch2's session to run tests
+    return Catch::Session().run(argc, argv);
+}
+
 TEST_CASE("Test C Get and To Substrait API", "[substrait-api]") {
   DuckDB db(nullptr);
-  db.LoadExtension<duckdb::DUCKDB_EXTENSION_CLASS>();
+  SubstraitExtension substrait_extension;
+  substrait_extension.Load(db);
   Connection con(db);
   con.EnableQueryVerification();
   // create the database
@@ -33,7 +36,8 @@ TEST_CASE("Test C Get and To Substrait API", "[substrait-api]") {
 
 TEST_CASE("Test C Get and To Json-Substrait API", "[substrait-api]") {
   DuckDB db(nullptr);
-  db.LoadExtension<duckdb::DUCKDB_EXTENSION_CLASS>();
+  SubstraitExtension substrait_extension;
+  substrait_extension.Load(db);
   Connection con(db);
   con.EnableQueryVerification();
   // create the database