def setUp(self):
        unittest.TestCase.setUp(self)

        # Put unit adapters on either side of a masking adapter to see if they
        # cooperate. Store meters in the raw context, push fathoms through the
        # mask, and expose feet to the outside world.
        self.units = units = {'in': meters, 'mid': fathom, 'out': feet}

        # Set up data for the contexts
        depth = Log(linspace(0.0, 100.0, 11), units=units['in'])
        lith = array(['sand'] * len(depth), dtype=object)

        # Create the contexts
        self.context = PassThruContext(ReductionContext(NumericContext()))
        self.raw_context = self.context.context_base

        # Add data (before creating the adapters)
        self.context.update(depth=depth, lith=lith)

        # (This simplifies creating UnitConversionAdapters)
        def always(value):
            class C(dict):
                def get(self, key, default=None):
                    return value

                def __repr__(self):
                    return '{*:%r}' % value

            return C()

        # Layer multiple adapters
        self.mask = (15.0 < depth) & (depth < 55.0)
        self.convert_out = lambda x: convert(x, units['in'], units['out'])
        self.convert_in = lambda x: convert(x, units['out'], units['in'])
        self.context.get_reduction_context(OpenContext).context_filter = \
            MaskFilter( mask = self.mask )