org.apache.cassandra.config.ConfigurationException: Saved cluster name X != configured name Test Cluster

Cassandra refuses to start:
org.apache.cassandra.config.ConfigurationException: Saved cluster name X != configured name Test Cluster

Explanation:
this means, "cluster_name" value in you cassandra configuration fille(Ubuntu: /etc/cassandra/cassandra.yaml) does not match the cluster name found in the data files..

Solution:
1. change the value of cluster_name in cassandra.yaml to fit the cluster name found in your data directory

2. OR delete all files in your data directory (Ubunut: /var/lib/cassandra/data/)... YOU WILL LOSE ALL data stored in cassandra!