add test for rstrip_end() in Text class
diff --git a/tests/test_text.py b/tests/test_text.py
index 432bc4a91..9419b2fbf 100644
--- a/tests/test_text.py
+++ b/tests/test_text.py
@@ -106,6 +106,12 @@ def test_rstrip():
     assert str(test) == "Hello, World!"
 
 
+def test_rstrip_end():
+    test = Text("Hello, World!    ")
+    test.rstrip_end(14)
+    assert str(test) == "Hello, World! "
+
+
 def test_stylize():
     test = Text("Hello, World!")
     test.stylize(7, 11, "bold")

## Type of changes

- [ ] Bug fix
- [ ] New feature
- [ ] Documentation / docstrings
- [x] Tests
- [ ] Other

## Checklist

- [x] I've run the latest [black](https://github.com/ambv/black) with default args on new code.
- [ ] I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
- [ ] I've added tests for new code.
- [x] I accept that @willmcgugan may be pedantic in the code review.

## Description

been looking at rich/text.py and found that tests for rstrip_end was missing, not sure why the coverage was 100% for text.py before then, now obviously is still 100% for the file. 

Changed file: tests/test_text.py

Also, 
1. I tried running `black . --check` but found that several other files needs reformatting, haven't pushed the reformatting changes yet, need to know your thoughts on that first:

![image](https://user-images.githubusercontent.com/50042066/87525240-ce447b80-c6bb-11ea-9683-4d4b3b74e879.png)

2. Looks like you forgot to add the return type for rstrip_end() ?
https://github.com/willmcgugan/rich/blob/e9e72000c50f56654c89e119ff882e322e51ecf3/rich/text.py#L415
https://github.com/willmcgugan/rich/blob/e9e72000c50f56654c89e119ff882e322e51ecf3/rich/text.py#L411