Increase coverage (#42)

* Introduce mocking framework and increase coverage (#22)

This change introduces two common golang patterns:

- types: this will allow fine-tuned control over imported
types by defining where they will be used and how

- mock: this allows the generation of mock constructors,
which allows for testing any individual path in a method by
"injecting" a mock method which matches the expected type

This change also increases test coverage to 100%

Co-authored-by: Yoshiyuki Mineo <Yoshiyuki.Mineo@jp.sony.com>

* gofmt

---------

Co-authored-by: Bradley Boutcher <btboutcher@icloud.com>

types/types.go

@@ -0,0 +1,8 @@
+// Package Types defines type signatures used throughout SonyFlake. This allows for
+// fine-tuned control over imports, and the ability to mock out imports as well
+package types
+
+import "net"
+
+// InterfaceAddrs defines the interface used for retrieving network addresses
+type InterfaceAddrs func() ([]net.Addr, error)