check if volume for the secret is properly mounted.
$ kubectl exec mypod ls /etc/foo
password
username
$ kubectl exec mypod cat /etc/foo/username
admin
$ kubectl exec mypod cat /etc/foo/password
1f2d1e2e67df

check if env (environment variable) for the secret is properly assigned.
$ kubectl exec secret-env-pod env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=secret-env-pod
SECRET_USERNAME=admin
SECRET_PASSWORD=1f2d1e2e67df
