Add COO accessor tests

[KyleVaughn]

Description:

There needs to be unit tests to determine if the library is able to able to get information about matrices in the COO format. This unit test information will be important ensure that information about matrices in the COO format can be accessed to be used in other COO format operations for a variety of test cases.

Tasks:

• [ ] Test that the implementation can return the number of rows for a COO format matrix
• [ ] Test that the implementation can return the number of columns for a COO format matrix
• [ ] Test that the implementation can return an element value at given row and column index values for a matrix in the COO format
• [ ] Test that the implementation can return a "COO" label for matrices in the COO format
• [ ] Test that the implementation can identify invalid inputs and return a proper error message

Definition of done:

Evidence of a functional unit test code file that tests if a provided accessor function is able to return index, size, coefficient, and format information about matrices in the COO format

[KyleVaughn]

Review by @prathameshnakhate

[prathameshnakhate]

The description seems well-defined. In tasks, we can also have a test to check if the state of the matrix is returned correctly.

[prathameshnakhate]

Also, you can place this issue in the Kanban board. I think the "Created" label should be appropriate for this issue. After we have finalized all the tasks and are ready for implementation, we can change the label to "Accepted"