FixedProbabilityConnector sometimes overflow
found with 
https://github.com/SpiNNakerManchester/sPyNNaker/blob/master/unittests/model_tests/test_connectors.py
 
in rare but not zero case the asserts 
            assert max(source_histogram) <= max_row_length
            assert max(target_histogram) <= max_col_length
Fail.

Passing a constant seed into FixedProbabilityConnector is NOT a FIX!

We need to decide between
1. have an actual max 
2. Capping to the utility_calls.get_probable_maximum_selected value
3.Capping to the higher of utility_calls.get_probable_maximum_selected or some user specified value.
a. in a config
b. as an extra parameter to the connector

Could be related to:
https://github.com/SpiNNakerManchester/sPyNNaker/issues/585


diff --git a/spynnaker/pyNN/models/neural_projections/connectors/fixed_number_post_connector.py b/spynnaker/pyNN/models/neural_projections/connectors/fixed_number_post_connector.py
index c2f1df1e22..4200d5ea4d 100644
--- a/spynnaker/pyNN/models/neural_projections/connectors/fixed_number_post_connector.py
+++ b/spynnaker/pyNN/models/neural_projections/connectors/fixed_number_post_connector.py
@@ -184,7 +184,7 @@ class FixedNumberPostConnector(AbstractGenerateConnectorOnMachine):
         selection_prob = 1.0 / float(synapse_info.n_post_neurons)
         n_connections = utility_calls.get_probable_maximum_selected(
             synapse_info.n_pre_neurons * synapse_info.n_post_neurons,
-            self.__n_post, selection_prob,
+            self.__n_post * synapse_info.n_pre_neurons, selection_prob,
             chance=1.0/100000.0)
         return int(math.ceil(n_connections))
 
diff --git a/unittests/model_tests/test_connectors.py b/unittests/model_tests/test_connectors.py
index b78cc6ab39..2753693ad5 100644
--- a/unittests/model_tests/test_connectors.py
+++ b/unittests/model_tests/test_connectors.py
@@ -22,7 +22,6 @@ from spynnaker.pyNN.models.neural_projections.connectors import (
     FixedNumberPreConnector, FixedNumberPostConnector,
     FixedProbabilityConnector, IndexBasedProbabilityConnector)
 from unittests.mocks import MockSimulator, MockPopulation, MockSynapseInfo
-from unittest import SkipTest
 
 
 @pytest.fixture(scope="module", params=[10, 100])
@@ -176,7 +175,5 @@ def test_connectors(
             print(max_col_length, max(target_histogram), target_histogram)
             print(max_weight, matrix_max_weight, synaptic_block["weight"])
             print(max_delay, matrix_max_delay, synaptic_block["delay"])
-            raise SkipTest(
-                "https://github.com/SpiNNakerManchester/sPyNNaker/issues/587")
     print(connector, n_pre, n_post, n_in_slice, max_row_length,
           max_source, max_col_length, max_target)
['spynnaker/pyNN/models/neural_projections/connectors/fixed_number_post_connector.py', 'unittests/model_tests/test_connectors.py']