Refactor decryption tests

[jbygdell]

Please describe the feature
As a developer, I want the tests to be limited in scope so that it is easy to see where a failure occurs, that includes having proper names for the tests.

Acceptance criteria

• Ensure all tests can be run in isolation
• Ensure all tests has relevance.
• Ensure all temp files are removed after the test has run.
• Split tests with multiple checks into separate tests.
• Each test file should only contain one test suite.
• Thing that can be shared between tests should be set up during the SetupSuite step.

Additional context

Estimation of size: small

Estimation of priority: low