Switch to ginkgo/gomega for tests

This switches over to ginkgo/gomega for tests, which makes writing
certain tests easier/more fluent in the future.

vendor/github.com/onsi/ginkgo/internal/leafnodes/interfaces.go

@@ -0,0 +1,19 @@
+package leafnodes
+
+import (
+	"github.com/onsi/ginkgo/types"
+)
+
+type BasicNode interface {
+	Type() types.SpecComponentType
+	Run() (types.SpecState, types.SpecFailure)
+	CodeLocation() types.CodeLocation
+}
+
+type SubjectNode interface {
+	BasicNode
+
+	Text() string
+	Flag() types.FlagType
+	Samples() int
+}