Add nop config provider

config/config_test.go

@@ -407,3 +407,16 @@ func TestEnvProviderWithEmptyPrefix(t *testing.T) {
 	scope := emptyScope.Get("key")
 	require.Equal(t, "value", scope.Get("").AsString())
 }
+
+func TestNopProvider_Get(t *testing.T) {
+	t.Parallel()
+	p := NopProvider{}
+	assert.Equal(t, "NopProvider", p.Name())
+	assert.NoError(t, p.RegisterChangeCallback("key", nil))
+	assert.NoError(t, p.UnregisterChangeCallback("token"))
+
+	v := p.Get("randomKey")
+	assert.Equal(t, "NopProvider", v.Source())
+	assert.True(t, v.HasValue())
+	assert.Nil(t, v.Value())
+}

config/nop_provider.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package config
+
+import "time"
+
+// NopProvider is an implementation of config provider that does nothing.
+// It should be used for testing purposes only.
+type NopProvider struct{}
+
+var _ Provider = (*NopProvider)(nil)
+
+// Name is NopProvider
+func (p NopProvider) Name() string {
+	return "NopProvider"
+}
+
+// Get returns an invalid Value.
+func (p NopProvider) Get(key string) Value {
+	return NewValue(p, key, nil, true, Invalid, &time.Time{})
+}
+
+// RegisterChangeCallback does nothing and simply returns nil.
+func (p NopProvider) RegisterChangeCallback(key string, callback ChangeCallback) error {
+	return nil
+}
+
+// UnregisterChangeCallback does nothing and simply returns nil.
+func (p NopProvider) UnregisterChangeCallback(token string) error {
+	return nil
+}