For training and testing, your directory structure should look like this
Datasets
├──train
└──Rain13K
├──input
└──target
└──test
├──Test100
├──input
└──target
├──Rain100H
├──input
└──target
├──Rain100L
├──input
└──target
├──Test1200
├──input
└──target
└──Test2800
├──input
└──target