给定一组文本，按照单词出现的频率降序对它们进行排序。
"this is a test string to test the frequency of each word"
Each: 1
Frequency: 1
String: 1
Test: 2
The: 1
This: 1
To: 1
Word: 1
A: 1
Is: 1
Of: 1
Sorting in descending order: 

Test: 2
Each: 1
Frequency: 1
String: 1
The: 1
This: 1
To: 1
Word: 1
A: 1
Is: 1
Of: 1