refactor-for-testability (#3)

Co-authored-by: jdl <jdl@desktop>
Co-authored-by: jdl <jdl@crumpington.com>
Reviewed-on: #3

peer/mock-iface_test.go

@@ -0,0 +1,31 @@
+package peer
+
+import "bytes"
+
+type TestIFace struct {
+	out *bytes.Buffer // Toward the network.
+	in  *bytes.Buffer // From the network
+}
+
+func NewTestIFace() *TestIFace {
+	return &TestIFace{
+		out: &bytes.Buffer{},
+		in:  &bytes.Buffer{},
+	}
+}
+
+func (iface *TestIFace) Write(b []byte) (int, error) {
+	return iface.in.Write(b)
+}
+
+func (iface *TestIFace) Read(b []byte) (int, error) {
+	return iface.out.Read(b)
+}
+
+func (iface *TestIFace) UserWrite(b []byte) (int, error) {
+	return iface.out.Write(b)
+}
+
+func (iface *TestIFace) UserRead(b []byte) (int, error) {
+	return iface.in.Read(b)
+}