Improved key tests

[shaspitz]

Description

Improves key tests s.t they would have caught bugs like this: #785

Type of change

• Refactor: Changes existing code style, naming, structure, etc.
• Testing: Adds testing

Regression tests

Existing key tests that were not touched

New behavior tests

New tests in keys_test.go

Versioning Implications

• This PR will affect semantic versioning as defined for ICS

If the above box is checked, which version should be bumped?

• MAJOR: Consensus breaking changes to both the provider and consumers(s), including updates/breaking changes to IBC communication between provider and consumer(s)
• MINOR: Consensus breaking changes which affect either only the provider or only the consumer(s)
• PATCH: Non consensus breaking changes

Targeting

Please select one of the following:

• This PR is only relevant to main
• This PR is relevant to main, and should also be back-ported to ____ (ex: v1.0.0 and v1.1.0)
• This PR is only relevant to ____ (ex: v1.0.0, v1.1.0, and v1.2.0)

[shaspitz]

@mpoke this PR will fail as expected until #786 is merged

[mpoke]

LGTM

[sainoe]

LGTM