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, 14 insertions, 0 deletions

diff --git a/python/tests/files/datacite/datacite_result_20.json b/python/tests/files/datacite/datacite_result_20.json
new file mode 100644
index 00000000..1868eede
--- /dev/null
+++ b/python/tests/files/datacite/datacite_result_20.json
@@ -0,0 +1,14 @@
+{
+    "extra": {},
+    "title": "<h1>Eastern questionnaire</h1>",
+    "release_type": "article",
+    "release_stage": "published",
+    "release_date": "2017-08-24",
+    "release_year": 2017,
+    "ext_ids": {
+        "doi": "10.7916/d86x0cg1"
+    },
+    "contribs": [],
+    "refs": [],
+    "abstracts": []
+}