How do I design objects using tests

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How do I design objects using tests @cocoders

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@cocoders Who I am? Developer, Former medieval reactor, Beer lover and founder of Cocoders

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Let's imagine legacy app: http://git.io/vLPVa @cocoders

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Task: Allow company to view incoming and outgoing invoices using system @cocoders

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The first attempt: http://git.io/vLPre @cocoders Design Invoice object

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Second attempt (encapsulation): http://git.io/vLPoh @cocoders Design Invoice object

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Another attempt (ValueObjects): http://git.io/vLPKZ @cocoders Design Invoice object

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InvoiceRegistry model concept: http://git.io/vLPPq @cocoders Design Model

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Use important concept in legacy: http://git.io/vLPXc @cocoders Design Model

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Protect object invariants: http://git.io/vLPXw @cocoders Design Model

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Implementation of model concept in separate mysql adapter: http://git.io/vLP1D @cocoders Design Model

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Application layer rely on abstraction: http://git.io/vLPM7 @cocoders Design Application

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Usage of application object in legacy app: http://git.io/vLPDE @cocoders Design Application