Refactor unit tests

[jcc37-zz]

In PR #46 , old tests are fixed and updated for the new data flow with dataset support. However, according to the comments from @Rhombus33 and @jnager , several code refactoring and changes are necessary to our current tests. These changes should implement the following items and be completed in one or more PRs:

• Test the user-facing behavior instead of part of the implementation (i.e. if the tabs div is present in the DOM)
• Assign literal values and anonymous functions to constants
• Separate tests of a component with different type variable parameters to distinct describe blocks
• Tests should import modules rather than declare components when setting up TestBed.
  • Should we rename xxx.component.spec.ts to xxx.module.spec.ts since we are now importing the entire module when testing?
• Check insistent tests related to observable subscription Fix undeterministic test failure #76

Before this issue gets resolved, tests should still be added and updated to each PR along with any new features or changes in the data flow.

[64json]

• Mocked dependencies: Multiple datasets support #46 (comment)

[64json]

• Arrange-Act-Assert structure: Multiple datasets support #46 (comment)