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, 28 insertions, 0 deletions

diff --git a/python/tests/files/datacite/datacite_result_13.json b/python/tests/files/datacite/datacite_result_13.json
new file mode 100644
index 00000000..3da3816d
--- /dev/null
+++ b/python/tests/files/datacite/datacite_result_13.json
@@ -0,0 +1,28 @@
+{
+    "extra": {},
+    "title": "[M\u00fcssen wir des Gl\u00fccks uns sch\u00e4men?]",
+    "release_type": "article-journal",
+    "release_stage": "published",
+    "release_date": "1940-10-05",
+    "release_year": 1940,
+    "ext_ids": {
+        "doi": "10.5169/seals-314104"
+    },
+    "publisher": "Buchdruckerei B\u00fcchler & Co.",
+    "contribs": [
+        {
+            "index": 0,
+            "raw_name": "O.M.",
+            "role": "author"
+        },
+        {
+            "index": 1,
+            "raw_name": "Hiltbrunner, Hermann",
+            "given_name": "Hermann",
+            "surname": "Hiltbrunner",
+            "role": "author"
+        }
+    ],
+    "refs": [],
+    "abstracts": []
+}
\ No newline at end of file