Update Tests

[alex-aaron]

Summary or Proposed Changes

• I want to update each _ method that requires the current index and array to be passed into the callback functions to check that those values are passed in correctly. I also want to update each _ method that requires the current key and object to be passed into callback functions to check those values as well.
• Add test to check that _.indexOf is being used in _.unique
• Add test to check that _.map is being used in _.pluck
• Install prettier and make formatting changes