datacite: add conversion fixtures

The `test_datacite_conversions` function will compare an input
(datacite) document to an expected output (release entity as JSON). This
way, it should not be too hard to add more cases by adding: input,
output - and by increasing the counter in the range loop within the
test.

To view input and result side by side with vim, change into the test
directory and run:

    tests/files/datacite $ ./caseview.sh 18

1 files changed, 44 insertions, 0 deletions

diff --git a/python/tests/files/datacite/datacite_doc_22.json b/python/tests/files/datacite/datacite_doc_22.json
new file mode 100644
index 00000000..42448ddf
--- /dev/null
+++ b/python/tests/files/datacite/datacite_doc_22.json
@@ -0,0 +1,44 @@
+{
+    "attributes": {
+      "doi": "10.7916/d86x0cg1",
+      "creators": [
+        {
+          "name": "Anton Welch",
+          "affiliation": [
+            "Department of pataphysics"
+          ],
+          "nameIdentifiers": []
+        }
+      ],
+      "titles": [
+        {
+          "title": "ABC"
+        }
+      ],
+      "publicationYear": 2017,
+      "language": "GERMAN",
+      "types": {
+        "ris": "GEN",
+        "bibtex": "misc",
+        "citeproc": "article",
+        "schemaOrg": "CreativeWork"
+      },
+      "dates": [
+        {
+          "date": "2017-08-24",
+          "dateType": "Created"
+        },
+        {
+          "date": "2019-08-04",
+          "dateType": "Updated"
+        },
+        {
+          "date": "2017",
+          "dateType": "Issued"
+        }
+      ],
+      "isActive": true,
+      "state": "findable"
+    }
+  }
+