Added validators (closes #59)

src/cpl_cli/validators/workspace_validator.py

@@ -0,0 +1,17 @@
+from cpl_cli import Error
+from cpl_cli.configuration import WorkspaceSettings
+from cpl_core.configuration.validator_abc import ValidatorABC
+
+
+class WorkspaceValidator(ValidatorABC):
+
+    def __init__(self, workspace: WorkspaceSettings):
+        self._workspace = workspace
+
+        ValidatorABC.__init__(self)
+
+    def validate(self) -> bool:
+        result = self._workspace is not None
+        if not result:
+            Error.error('The command requires to be run in an CPL workspace, but a workspace could not be found.')
+        return result