Test multiple C++ standards; move tests to top level

.gitignore

@@ -1 +1 @@
-/test/build/
+/build/

Makefile

@@ -1,7 +1,23 @@
-.PHONY: test
-test:
-	$(MAKE) -C test
+# This Makefile is entirely for running unit tests for rcp.h
+
+INCLUDE := include
+STANDARDS := 11 14 17 20 23
+BINARIES := $(addprefix build/tests-, $(STANDARDS))
+
+.PHONY: all
+all: $(BINARIES)
+	@for std in $(STANDARDS); do \
+		echo "=== Test C++$$std ==="; \
+		build/tests-$$std; \
+		valgrind --leak-check=full --error-exitcode=1 \
+			--log-file=build/valgrind-$$std.log build/tests-$$std \
+			|| { echo "valgrind failed for C++$$std (see build/valgrind-$$std.log)"; exit 1; }; \
+	done
+
+build/tests-%: tests.cpp $(INCLUDE)/rcp.h
+	@mkdir -p $(dir $@)
+	$(CXX) -std=c++$* -g -Wall -I$(INCLUDE) -o $@ $<
 
 .PHONY: clean
 clean:
-	$(MAKE) -C test clean
+	rm -rf build

test/Makefile

@@ -1,14 +0,0 @@
-INCLUDE := ../include
-
-.PHONY: all
-all: build/tests
-	build/tests
-	valgrind --leak-check=full --error-exitcode=1 --log-file=build/valgrind.log build/tests
-
-build/tests: tests.cpp $(INCLUDE)/rcp.h
-	mkdir -p $$(dirname $@)
-	$(CXX) -std=c++20 -g -Wall -I$(INCLUDE) -o $@ $<
-
-.PHONY: clean
-clean:
-	rm -rf build

tests.cpp

@@ -114,11 +114,11 @@ void test_multi_construct_from_raw_pointers()
 {
     Receiver r;
     auto myo = MyObj::create();
-    for (size_t i = 0u; i < 5u; i++)
+    for (int i = 0; i < 5; i++)
     {
         myo->add_to(r);
     }
-    for (size_t i = 0u; i < 5u; i++)
+    for (int i = 0; i < 5; i++)
     {
         assert(r.objects[i]->v == 42);
     }