add a roundtrip test for an empty anndata (#208)

tests/testthat/test-roundtrip-empty.R

@@ -0,0 +1,75 @@
+skip_if_no_anndata()
+skip_if_not_installed("reticulate")
+
+library(reticulate)
+testthat::skip_if_not(
+  reticulate::py_module_available("dummy_anndata"),
+  message = "Python dummy_anndata module not available for testing"
+)
+
+ad <- reticulate::import("anndata", convert = FALSE)
+bi <- reticulate::import_builtins()
+
+known_issues <- read_known_issues()
+
+# first generate a python h5ad
+adata_py <- ad$AnnData()
+
+name <- "empty"
+
+# create a couple of paths
+file_py <- withr::local_file(tempfile(paste0("anndata_py_", name), fileext = ".h5ad"))
+file_r <- withr::local_file(tempfile(paste0("anndata_r_", name), fileext = ".h5ad"))
+
+# write to file
+adata_py$write_h5ad(file_py)
+
+test_that(paste0("Reading an AnnData with layer '", name, "' works"), {
+  msg <- message_if_known(
+    backend = "HDF5AnnData",
+    slot = c("none"),
+    dtype = name,
+    process = "read",
+    known_issues = known_issues
+  )
+  skip_if(!is.null(msg), message = msg)
+
+  adata_r <- read_h5ad(file_py, to = "HDF5AnnData")
+  expect_equal(
+    adata_r$shape(),
+    unlist(reticulate::py_to_r(adata_py$shape))
+  )
+
+  # check that the print output is the same
+  str_r <- capture.output(print(adata_r))
+  str_py <- capture.output(print(adata_py))
+  expect_equal(str_r, str_py)
+})
+
+test_that(paste0("Writing an AnnData with layer '", name, "' works"), {
+  msg <- message_if_known(
+    backend = "HDF5AnnData",
+    slot = c("none"),
+    dtype = name,
+    process = c("read", "write"),
+    known_issues = known_issues
+  )
+  skip_if(!is.null(msg), message = msg)
+
+  adata_r <- read_h5ad(file_py, to = "InMemoryAnnData")
+  write_h5ad(adata_r, file_r)
+
+  # read from file
+  adata_py2 <- ad$read_h5ad(file_r)
+
+  # check that the print output is the same
+  expect_equal(
+    unlist(reticulate::py_to_r(adata_py2$shape)),
+    unlist(reticulate::py_to_r(adata_py$shape))
+  )
+
+  # check that the print output is the same
+  str_py2 <- capture.output(print(adata_py2))
+  str_py <- capture.output(print(adata_py))
+  expect_equal(str_py2, str_py)
+})