Add mutateSource containing function tests.
Add mutateSource local identifier test.
Add mutateSource parameter extraction tests.
Add mutateFunctionDeclaration test.
Add mutateIdentifier tests.
Refactor falafel AST node retrieval in tests.
Add mutateMemberExpression test.
Add mutateVariableDeclaration test.
Add mutateSource.swapMongoCalls test.
Merge pull request #113 from mcomella/test_mutate

Test mutateSource module.