Add NewAtomicLevelAt helper function (#411)

Add a helper for the common new-and-set pattern.

config.go

@@ -100,7 +100,7 @@ func NewProductionEncoderConfig() zapcore.EncoderConfig {
 // Stacktraces are automatically included on logs of ErrorLevel and above.
 func NewProductionConfig() Config {
 	return Config{
-		Level:       NewAtomicLevel(),
+		Level:       NewAtomicLevelAt(InfoLevel),
 		Development: false,
 		Sampling: &SamplingConfig{
 			Initial:    100,
@@ -138,11 +138,8 @@ func NewDevelopmentEncoderConfig() zapcore.EncoderConfig {
 // console encoder, writes to standard error, and disables sampling.
 // Stacktraces are automatically included on logs of WarnLevel and above.
 func NewDevelopmentConfig() Config {
-	dyn := NewAtomicLevel()
-	dyn.SetLevel(DebugLevel)
-
 	return Config{
-		Level:            dyn,
+		Level:            NewAtomicLevelAt(DebugLevel),
 		Development:      true,
 		Encoding:         "console",
 		EncoderConfig:    NewDevelopmentEncoderConfig(),

level.go

@@ -74,6 +74,14 @@ func NewAtomicLevel() AtomicLevel {
 	}
 }
 
+// NewAtomicLevelAt is a convienence function that creates an AtomicLevel
+// and then calls SetLevel with the given level.
+func NewAtomicLevelAt(l zapcore.Level) AtomicLevel {
+	a := NewAtomicLevel()
+	a.SetLevel(l)
+	return a
+}
+
 // Enabled implements the zapcore.LevelEnabler interface, which allows the
 // AtomicLevel to be used in place of traditional static levels.
 func (lvl AtomicLevel) Enabled(l zapcore.Level) bool {

level_test.go

@@ -53,6 +53,8 @@ func TestNewAtomicLevel(t *testing.T) {
 	assert.Equal(t, InfoLevel, lvl.Level(), "Unexpected initial level.")
 	lvl.SetLevel(ErrorLevel)
 	assert.Equal(t, ErrorLevel, lvl.Level(), "Unexpected level after SetLevel.")
+	lvl = NewAtomicLevelAt(WarnLevel)
+	assert.Equal(t, WarnLevel, lvl.Level(), "Unexpected level after SetLevel.")
 }
 
 func TestAtomicLevelMutation(t *testing.T) {