[Python] removing of unnecessary spaces in text

Could you please shed some light on this?
The spaces are not dealt properly (test C and E) and I don't understand what is wrong.
Thanks a lot.

foo={'testing':['this is test A',' this is test B',' this is test C ',' this is test D',' this is test E ']}
foo=pd.DataFrame(foo,columns=['testing'])
print("Before:")
print(foo,"\n")
foo.replace(r'\s+', ' ', regex=True,inplace=True)
print("After:")
print(foo)

Before:
testing
0 this is test A
1 this is test B
2 this is test C
3 this is test D
4 this is test E

After:
testing
0 this is test A
1 this is test B
2 this is test C
3 this is test D
4 this is test E

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