Question

I’m starting some testing using Mockito on some service classes I use for connecting to my data store. I now want to determine the best practice way writing tests for it. The principle is for each entity there is a way to list, add, delete etc a row from the data store(mongo/mysql etc) for a specific entity.

Take this class that allows me to talk to my database that stores a list of companies

public class CompanyService extends Service{
    public CompanyService() {
        ...
    }

    public saveCompany(Company company) {
         ...
    }

     // get a list of all companies
    public List<Company> getCompanies() {

         List<Company> companies = new ArrayList<Company>();

         try {
             CompanyResult<Rows<String, String>> rows = db.query(....); 

             for (Row<String, String> row : rows.getResult()) {
                 companies.add(row.getColumns());
             }
         catch (Exception e){
            logger.warn("Error retrieving companies", e);
         }

    }

}

What exactly should I test in the getCompanies method and how can I use Mockito to do it?

Answer 1

Your System Under Test is the Company Service. You want to test that, assuming all its dependencies/collaborators function properly, it functions properly.

The db object looks like the only dependency/collaborator you need to worry about within the getCompanies() method. Use Mockito to mock the call to db.query()

You could set up a test method like so:

@Test
public void testGetCompanies() {
  /*** Arraign ***/
  CompanyService cs = new CompanyService();

  // Setup mock db
  DB mockDb = mock(DB.class);

  // Setup fake results for query
  CompanyResult<Rows<String, String>> sampleResults = ... // build sample results here

  // Have query on mock return fake results
  when(db.query(/* match arguments */)).thenReturn(sampleResults);

  // Tell your System Under Test to use the mock collaborator
  cs.setDB(mockDb);

  /*** Act ***/
  CompanyResult<Rows<String, String>> results = cs.getCompanies();

  /*** Assert ***/
  ... // Test that results and sampleResults are effectively the same
}