Added test

logrus_test.go

@@ -98,3 +98,33 @@ func TestInfoShouldNotAddSpacesBetweenStrings(t *testing.T) {
 		assert.Equal(t, fields["msg"], "testtest")
 	})
 }
+
+func TestWithFieldsShouldAllowAssignments(t *testing.T) {
+	var buffer bytes.Buffer
+	var fields Fields
+
+	logger := New()
+	logger.Out = &buffer
+	logger.Formatter = new(JSONFormatter)
+
+	localLog := logger.WithFields(Fields{
+		"key1": "value1",
+	})
+
+	localLog.WithField("key2", "value2").Info("test")
+	err := json.Unmarshal(buffer.Bytes(), &fields)
+	assert.Nil(t, err)
+
+	assert.Equal(t, "value2", fields["key2"])
+	assert.Equal(t, "value1", fields["key1"])
+
+	buffer = bytes.Buffer{}
+	fields = Fields{}
+	localLog.Info("test")
+	err = json.Unmarshal(buffer.Bytes(), &fields)
+	assert.Nil(t, err)
+
+	_, ok := fields["key2"]
+	assert.Equal(t, false, ok)
+	assert.Equal(t, "value1", fields["key1"])
+}