bring back test in config as well

component/config.go

@@ -27,7 +27,7 @@ type Config any
 var configValidatorType = reflect.TypeOf((*ConfigValidator)(nil)).Elem()
 
 // UnmarshalConfig helper function to UnmarshalConfig a Config.
-// Deprecated: [v0.97.0] Use conf.Unmarshal(&intoCfg)
+// Deprecated: [v0.99.0] Use conf.Unmarshal(&intoCfg)
 func UnmarshalConfig(conf *confmap.Conf, intoCfg Config) error {
 	return conf.Unmarshal(intoCfg)
 }

component/config_test.go

@@ -12,6 +12,8 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/confmap"
 )
 
 var _ fmt.Stringer = Type{}
@@ -420,3 +422,27 @@ func TestNewType(t *testing.T) {
 		})
 	}
 }
+
+type configWithEmbeddedStruct struct {
+	String                      string `mapstructure:"string"`
+	Num                         int    `mapstructure:"num"`
+	EmbeddedUnmarshallingConfig `mapstructure:",squash"`
+}
+
+type EmbeddedUnmarshallingConfig struct {
+}
+
+func (euc *EmbeddedUnmarshallingConfig) Unmarshal(_ *confmap.Conf) error {
+	return nil // do nothing.
+}
+func TestStructWithEmbeddedUnmarshaling(t *testing.T) {
+	cfgMap := confmap.NewFromStringMap(map[string]any{
+		"string": "foo",
+		"num":    123,
+	})
+	tc := &configWithEmbeddedStruct{}
+	err := UnmarshalConfig(cfgMap, tc)
+	require.NoError(t, err)
+	assert.Equal(t, "foo", tc.String)
+	assert.Equal(t, 123, tc.Num)
+}