Added test for Legendre scattering - current tests converted all legenres to tabular distributions, this avoids that

tests/test_mg_legendre/inputs_true.dat

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+<?xml version='1.0' encoding='utf-8'?>
+<geometry>
+    <cell id="10000" material="10000" region="10000 -10001 10002 -10003 10004 -10005" universe="0" />
+    <cell id="10001" material="10001" region="10000 -10001 10002 -10003 10005 -10006" universe="0" />
+    <cell id="10002" material="10002" region="10000 -10001 10002 -10003 10006 -10007" universe="0" />
+    <surface boundary="reflective" coeffs="0.0" id="10000" type="x-plane" />
+    <surface boundary="reflective" coeffs="10.0" id="10001" type="x-plane" />
+    <surface boundary="reflective" coeffs="0.0" id="10002" type="y-plane" />
+    <surface boundary="reflective" coeffs="10.0" id="10003" type="y-plane" />
+    <surface boundary="reflective" coeffs="0.0" id="10004" type="z-plane" />
+    <surface coeffs="1.6667" id="10005" type="z-plane" />
+    <surface coeffs="3.3334" id="10006" type="z-plane" />
+    <surface boundary="reflective" coeffs="5.0" id="10007" type="z-plane" />
+</geometry>
+<?xml version='1.0' encoding='utf-8'?>
+<materials>
+    <cross_sections>../1d_mgxs.h5</cross_sections>
+    <material id="10000" name="1">
+        <density units="macro" value="1.0" />
+        <macroscopic name="uo2_iso" />
+    </material>
+    <material id="10001" name="2">
+        <density units="macro" value="1.0" />
+        <macroscopic name="clad_iso" />
+    </material>
+    <material id="10002" name="3">
+        <density units="macro" value="1.0" />
+        <macroscopic name="lwtr_iso" />
+    </material>
+</materials>
+<?xml version='1.0' encoding='utf-8'?>
+<settings>
+    <eigenvalue>
+        <particles>100</particles>
+        <batches>10</batches>
+        <inactive>5</inactive>
+    </eigenvalue>
+    <source strength="1.0">
+        <space type="box">
+            <parameters>0.0 0.0 0.0 10.0 10.0 5.0</parameters>
+        </space>
+    </source>
+    <energy_mode>multi-group</energy_mode>
+    <tabular_legendre>
+        <enable>false</enable>
+    </tabular_legendre>
+</settings>

tests/test_mg_legendre/results_true.dat

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+k-combined:
+1.110122E+00 2.549637E-02

tests/test_mg_legendre/test_mg_legendre.py

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+#!/usr/bin/env python
+
+import os
+import sys
+
+sys.path.insert(0, os.pardir)
+from testing_harness import PyAPITestHarness
+from input_set import MGInputSet
+
+
+class MGMaxOrderTestHarness(PyAPITestHarness):
+    def __init__(self, statepoint_name, tallies_present, mg=False):
+        PyAPITestHarness.__init__(self, statepoint_name, tallies_present)
+        self._input_set = MGInputSet()
+
+    def _build_inputs(self):
+        """Write input XML files."""
+        reps = ['iso']
+        self._input_set.build_default_materials_and_geometry(reps=reps)
+        self._input_set.build_default_settings()
+        # Enforce Legendre scattering
+        self._input_set.settings.tabular_legendre = {'enable': False}
+        self._input_set.export()
+
+
+if __name__ == '__main__':
+    harness = MGMaxOrderTestHarness('statepoint.10.*', False, mg=True)
+    harness.main()