Fixed string length check in LayerMapping

class City(NamedModel):

    name_txt = models.TextField(default='')

    name_short = models.CharField(max_length=5)

    population = models.IntegerField()

    density = models.DecimalField(max_digits=7, decimal_places=1)

    dt = models.DateField()

if HAS_GDAL:

    from django.contrib.gis.utils.layermapping import (LayerMapping,

        LayerMapError, InvalidDecimal, MissingForeignKey)

        LayerMapError, InvalidDecimal, InvalidString, MissingForeignKey)

    from django.contrib.gis.gdal import DataSource

    from .models import (

                          source_srs=4326)

        lm.save(silent=True)

    def test_charfield_too_short(self):

        mapping = copy(city_mapping)

        mapping['name_short'] = 'Name'

        lm = LayerMapping(City, city_shp, mapping)

        with self.assertRaises(InvalidString):

            lm.save(silent=True, strict=True)

    def test_textfield(self):

        "Tests that String content fits also in a TextField"

        mapping = copy(city_mapping)