Update `valid_header` to pass check for duplicated headers

1 files changed, 10 insertions, 1 deletions

diff --git a/quality_control/headers.py b/quality_control/headers.py
index 59d3d77..b7bc01e 100644
--- a/quality_control/headers.py
+++ b/quality_control/headers.py
@@ -1,6 +1,6 @@
 """Validate the headers"""
 
-from quality_control.errors import InvalidHeaderValue
+from quality_control.errors import DuplicateHeader, InvalidHeaderValue
 
 def valid_header(strains, headers):
     "Return the valid headers with reference to strains or throw an error"
@@ -13,4 +13,13 @@ def valid_header(strains, headers):
         raise InvalidHeaderValue(
             *(f"'{header}' not a valid strain." for header in invalid_headers))
 
+    unique_headers = set(headers)
+    if len(unique_headers) != len(headers):
+        repeated = (
+            (header, headers.count(header))
+            for header in unique_headers if headers.count(header) > 1)
+        raise DuplicateHeader(*(
+            f"'{header}' is present in the header row {times} times."
+            for header, times in repeated))
+
     return headers