Add low-level Julia test

CMakeLists.txt

@@ -652,6 +652,14 @@ if(openPMD_HAVE_JULIA)
         POSITION_INDEPENDENT_CODE ON
         WINDOWS_EXPORT_ALL_SYMBOLS ON
     )
+
+    add_test(NAME CLI.julia_lowlevel
+        COMMAND julia
+            ${openPMD_SOURCE_DIR}/test/julia/lowlevel_test.jl
+            ${openPMD_LIBRARY_OUTPUT_DIRECTORY}/libopenPMD.jl.so
+        WORKING_DIRECTORY
+            ${openPMD_RUNTIME_OUTPUT_DIRECTORY}
+    )
 endif()
 
 # python bindings

test/julia/lowlevel_test.jl

@@ -0,0 +1,35 @@
+import Base
+
+# pass as first argument the path to libopenPMD.jl.so
+
+module openPMD
+using CxxWrap
+@wrapmodule(ARGS[1])
+
+function __init__()
+    @initcxx
+end
+end
+
+s = openPMD.CXX_Series(
+    "../samples/lowlevel_julia_test.json", openPMD.ACCESS_CREATE)
+
+function Base.getindex(
+    cont::Cont,
+    index,
+) where
+{
+    A,
+    B,
+    Cont<:openPMD.CXX_Container{A,B}
+}
+    return openPMD.cxx_getindex(cont, index)
+end
+
+iteration = openPMD.cxx_iterations(s)[100]
+mesh = openPMD.cxx_meshes(iteration)
+# empty brackets to dereference CxxRef
+# automatic dereferencing works only for Int types since CxxRwap.jl defines
+# Base.getindex(x::CxxBaseRef, i::Int) = Base.getindex(x[], i)
+mesh[]["E"][]["x"]
+openPMD.cxx_flush(s, "{}")