从一段文本中提取所有的单词，并计算每个单词出现的次数。
This is a test sentence. This sentence is for testing purposes only.
单词列表为：["This", "is", "a", "test", "sentence", "This", "sentence", "is", "for", "testing", "purposes", "only"]
每个单词出现的次数为：
- This: 2
- is: 2
- a: 1
- test: 1
- sentence: 2
- for: 1
- testing: 1
- purposes: 1
- only: 1