Add DEN accessor tests

[KyleVaughn]

Description:

Create a test for the dense matrix accessor functions. These functions should be able to obtain information on the dense matrix format specifically. These tests are necessary to ensure proper implementation of accessor function to be used in other dense matrix operations.

Tasks:

• [x] Determine what kind of accessors are implemented
  • [x] Determine input/outpus arguments of each accessor function for the dense matrix
  • [x] Implement/declare a accessorDenTest() function into the source file for tests
  • [x] Create test to assert correct indexing of variables in DEN matrix
  • [x] Create test to assert that matrix is actually dense (zeros at non non-zero indices)
  • [x] Create test to assert that matrix size matches the inputted matrix size MxN
  • [x] Ensure that accessor functions work with matrix with "DEN" label/class
  • [x] Output error or pass messages for each test

    Definition of done:

    Ensure the code runs and is able to conduct test on the DEN accessor. Pass tests such as correct matrix size reads, correct value indexing and value display, and correct matrix storage type. Implement review feedback. Ensure all blocking tasks are completed beforehand. Examples of blocking issues: DEN class and matrix construction must be implemeted, along with accessor functions (can't test them if they don't exist!)

[KyleVaughn]

Review by @carltonjames

[carltonjames]

@nzamb222 This issue looks good. The problem is clearly defined, the stated tasks are cohesive, and the 'definition of done' is succinct. Nice work.