Add basic unit tests

[Asone]

There's currently no unit testing onto the API demo.

At some point, it'd be nice to have those as it would :
1/ Ensure that the demo works as expected
2/ Give example of the different use cases handling to users
3/ Show how to unit test that kind of app

The first step would be to build simple unit test covering :
1/ Juniper
2/ Rocket
3/ Diesel
4/ Lnd Mock

[Asone]

Unit test to do with expected complexity

• Test HTTP routes : Many examples of unit tests around Rocket routes probably exists to start writing tests quickly
• Test Diesel methods : Will require to build a test environment for database
• Test Juniper methods : Will require diesel methods to be mocked
• Test Invoice methods : No mock exists for lnd wrapper, will require to build one.

[Asone]

A few notes regarding unit & integration tests with rustlang and the different aspects of it.

• Testing diesel methods : Digging in issues and docs i found some examples on how to bootstrap a database for testing database transactions.

However, the current drafted solution can only create and drop the test database for EACH test. This makes the solution quite slow and painful :

• For each test we create a database
• Then run the migrations
• and then import the fixtures

This is an acceptable solution for small test suites, however this definitely can't be considered as a viable solution for long term development.

Unfortunately there is no way to perform operations prior a test suite with cargo for now. A hacky option could be the following one however : https://www.reddit.com/r/rust/comments/9wixkj/how_can_i_run_something_prior_to_all_cargo_tests/

[Asone]

Unfortunately there is no way to perform operations prior a test suite with cargo for now. A hacky option could be the following one however : https://www.reddit.com/r/rust/comments/9wixkj/how_can_i_run_something_prior_to_all_cargo_tests/

It appears that unfortunately the statics don't get a Drop call, which means our temporary test database will never be destroyed.

In order to avoir previous data to remain we could switch to a static name of database and drop previous database on each start of tests