validation: check for whitespaces in the image specification

addresses reanahub/reana-job-controller#364

CHANGES.rst

@@ -5,6 +5,7 @@ Version 0.9.0 (UNRELEASED)
 --------------------------
 
 - Changes REANA specification loading and validation functionality by porting some of the logic to ``reana-commons``.
+- Fixes ``validate --environment`` command to detect illegal white space characters in image names.
 
 Version 0.8.2 (UNRELEASED)
 --------------------------

reana_client/validation/environments.py

@@ -186,6 +186,10 @@ def _validate_image_tag(self, image):
             "type": "success",
             "message": "Environment image {} has the correct format.".format(image),
         }
+        if " " in image:
+            raise EnvironmentValidationError(
+                f"Environment image '{image}' contains illegal characters."
+            )
         if ":" in image:
             environment = image.split(":", 1)
             image_name, image_tag = environment[0], environment[-1]

tests/test_validate_environments.py

@@ -25,6 +25,7 @@
         ("foo:master", "tag is not recommended", False),
         ("foo:bar:baz", "has invalid tag", True),
         ("foo:bar:", "has invalid tag", True),
+        ("foo:bar ", "contains illegal characters", True),
     ],
 )
 def test_validate_environment_image_tag(image, output, exit_):