Resolve "observation_tests"

Closes #6 (closed)

added 4 commits

• c45755f7 - [test] added get observations by idx and sat
• ab853b0c - [test] add observation.data()
• ebef2b76 - [test] hassatellite
• 37b79819 - [test] common observations

Compare with previous version

assigned to @jmarti

This is ready to merge. @joanvallve , could you please take a look if you agree with the tests implemented? In case you do, you can merge it yourself.

unmarked as a Work In Progress

merged

mentioned in commit d5dada01