fix: test errors and ensure string gets encode into bytes as utf-8

Author: satra

nipype/interfaces/base.py

@@ -1285,9 +1285,13 @@ def _process(drain=0):
         result['stdout'] = []
         result['stderr'] = []
         result['merged'] = ''
-    runtime.stderr = bytes('\n'.join(result['stderr'])).decode('utf-8')
-    runtime.stdout = bytes('\n'.join(result['stdout'])).decode('utf-8')
-    runtime.merged = [bytes(val).decode('utf-8') for val in result['merged']]
+    runtime.stderr = bytes('\n'.join(result['stderr']), 'utf-8').decode('utf-8')
+    runtime.stdout = bytes('\n'.join(result['stdout']), 'utf-8').decode('utf-8')
+    if isinstance(result['merged'], list):
+        runtime.merged = [bytes(val).decode('utf-8')
+                          for val in result['merged']]
+    else:
+        runtime.merged = result['merged']
     runtime.returncode = proc.returncode
     return runtime