Don't add extra key "Column" to dict if there are no changes

gn3/csvcmp.py (csv_diff): If the diff is empty, don't add an extra key
"Column" to the dictionary.
tests/unit/test_csvcmp (test_csv_diff_only_column_change): Add test-case for
the above.

2 files changed, 24 insertions, 1 deletions

diff --git a/gn3/csvcmp.py b/gn3/csvcmp.py
index 453c97a..ebd323e 100644
--- a/gn3/csvcmp.py
+++ b/gn3/csvcmp.py
@@ -66,7 +66,8 @@ def csv_diff(base_csv, delta_csv, tmp_dir="/tmp"):
                       "--format json"))
     if _r.get("code") == 0:
         _r = json.loads(_r.get("output"))
-        _r["Columns"] = max(base_csv_header, delta_csv_header)
+        if any(_r.values()):
+            _r["Columns"] = max(base_csv_header, delta_csv_header)
     else:
         _r = {}
 
diff --git a/tests/unit/test_csvcmp.py b/tests/unit/test_csvcmp.py
index 023415d..4a96f99 100644
--- a/tests/unit/test_csvcmp.py
+++ b/tests/unit/test_csvcmp.py
@@ -77,3 +77,25 @@ BXD15,14,x,x"""
                         'Deletions': [],
                         'Modifications': [{'Current': 'BXD12,16,x,x,1',
                                            'Original': 'BXD12,16,x,x,x'}]})
+
+
+@pytest.mark.unit_test
+def test_csv_diff_only_column_change():
+    base_csv = """
+Strain Name,Value,SE,Count
+BXD1,18,x,0
+BXD12,16,x,x
+BXD14,15,x,x
+BXD15,14,x,x
+"""
+    delta_csv = """Strain Name,Value,SE,Count,Sex
+BXD1,18,x,0
+BXD12,16,x,x
+BXD14,15,x,x
+BXD15,14,x,x
+"""
+    assert(csv_diff(base_csv=base_csv,
+                    delta_csv=delta_csv) == {
+                        'Additions': [],
+                        'Deletions': [],
+                        'Modifications': []})