Implement casting of *Entry to error.

entry_test.go

@@ -8,6 +8,23 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+var err = fmt.Errorf("kaboom at layer %d", 4711)
+
+func TestToError(t *testing.T) {
+
+	assert := assert.New(t)
+
+	ctx := WithField("foo", "bar")
+	assert.Equal(nil, ctx.Debug("Hello").ToError())
+
+	ctx.Data[ErrorKey] = "error"
+	assert.Equal(nil, ctx.Debug("Hello").ToError())
+
+	ctx = ctx.WithError(err)
+	assert.Equal(err, ctx.Debug("Hello").ToError())
+
+}
+
 func TestEntryWithError(t *testing.T) {
 
 	assert := assert.New(t)
@@ -16,8 +33,6 @@ func TestEntryWithError(t *testing.T) {
 		ErrorKey = "error"
 	}()
 
-	err := fmt.Errorf("kaboom at layer %d", 4711)
-
 	assert.Equal(err, WithError(err).Data["error"])
 
 	logger := New()