VScode version: 1.36.1
ms-python.python: 2019.6.24221
Microsoft Python Language Server version 0.3.43.0
In the terminal I have a virtual environment which was set by conda with Python version 3.7.3. The packages in the environment were installed from a requirements.txt file:
dvc[s3]==0.51.2
click==7.0
numpy==1.16.4
pandas==0.24.2
pyarrow==0.14.0
dask[complete]==2.1.0
graphviz==0.11.1
In the following,

I was expecting to see the suggestion for .testing and not only for test. Is it a bug or a problem in my settings?
This looks like a bug. Thanks for reporting it. We will investigate.
Same as #1301

0.4.26+
What does 0.4.26+ mean? Will it be available with the next release of vscode?
The build with the fix is 0.4.26, so the fix will be available in 0.4.26 and above. The language server is released independently from VS Code or the Python extension and this update will be pushed out to everyone once we've had time to verify there aren't any problems. If you want to test early builds before then, you can use one of the other download channels, beta or daily:
"python.analysis.downloadChannel": "beta"
"python.analysis.downloadChannel": "daily"
Which will get the fix sooner (not just now, we're still working on building it).