diff --git a/tests/test_validate_network.py b/tests/test_validate_network.py
new file mode 100644
index 0000000..95a9362
--- /dev/null
+++ b/tests/test_validate_network.py
@@ -0,0 +1,119 @@
+"""Synthetic fixtures: no company INP or network data is embedded in tests."""
+import hashlib
+import importlib.util
+import json
+from pathlib import Path
+import tempfile
+import unittest
+
+spec=importlib.util.spec_from_file_location('validator',Path(__file__).resolve().parents[1]/'tools/validate_network.py')
+validator=importlib.util.module_from_spec(spec)
+spec.loader.exec_module(validator)
+
+INP='''[OPTIONS]
+FLOW_UNITS CMS
+LINK_OFFSETS DEPTH
+[JUNCTIONS]
+A 10 3 0 0 0
+B 9 4 0 0 0
+[CONDUITS]
+P A B 5 0.015 0.2 0.1 0 0
+[XSECTIONS]
+P CIRCULAR 0.6 0 0 0 1
+[COORDINATES]
+A 0 0
+B 3 4
+'''
+
+
+def fixture(text=INP):
+    return {'meta':{'sha256':hashlib.sha256(text.encode()).hexdigest(),'flowUnits':'CMS',
+                    'offsetMode':'DEPTH','physicalConversion':1},
+            'nodes':[{'id':'A','type':'junction','line':5,'raw':'A 10 3 0 0 0'.split(),
+                      'invert':10,'maxDepth':3,'top':13,'xy':[0,0],'connections':['P']},
+                     {'id':'B','type':'junction','line':6,'raw':'B 9 4 0 0 0'.split(),
+                      'invert':9,'maxDepth':4,'top':13,'xy':[3,4],'connections':['P']}],
+            'links':[{'id':'P','type':'conduit','line':8,'raw':'P A B 5 0.015 0.2 0.1 0 0'.split(),
+                      'fromNode':'A','toNode':'B','vertices':[],'pathXY':[[0,0],[3,4]],
+                      'planDistance':5,'length':5,'roughness':.015,'inletOffset':.2,'outletOffset':.1,
+                      'invertStart':10.2,'invertEnd':9.1,'centerStart':10.5,'centerEnd':9.4,
+                      'lengthDelta':0,'lengthDifferenceRatio':0,'slopeInput':.22,'slopePlan':.22,
+                      'renderable':True,'section':{'shape':'CIRCULAR','height':.6,'width':.6,
+                       'diameter':.6,'barrels':1,'raw':'P CIRCULAR 0.6 0 0 0 1'.split()}}],
+            'summary':{'counts':{'junction':2,'outfall':0,'storage':0,'conduit':1,'pump':0,'weir':0},
+                       'coordinateCount':2,'shapes':{'CIRCULAR':1},'renderedConduits':1,'vertexCount':0},'issues':[]}
+
+
+class ValidationTests(unittest.TestCase):
+    def run_case(self,data=None,text=INP):
+        with tempfile.TemporaryDirectory() as folder:
+            root=Path(folder)
+            (root/'source.inp').write_bytes(text.encode())
+            (root/'network.json').write_text(json.dumps(data or fixture(text)),encoding='utf8')
+            return validator.validate(root/'source.inp',root/'network.json')
+
+    def test_matching_fixture(self):
+        self.assertEqual(self.run_case()['status'],'passed')
+
+    def test_changed_diameter_is_caught(self):
+        data=fixture();data['links'][0]['section']['diameter']=.9
+        result=self.run_case(data)
+        self.assertEqual(result['status'],'failed')
+        self.assertIn('section.diameter',[e['field'] for e in result['mismatches']])
+
+    def test_changed_connection_is_caught(self):
+        data=fixture();data['links'][0]['toNode']='A'
+        self.assertEqual(self.run_case(data)['status'],'failed')
+
+    def test_missing_facility_is_caught(self):
+        data=fixture();data['nodes'].pop()
+        self.assertEqual(self.run_case(data)['status'],'failed')
+
+    def test_null_is_not_zero(self):
+        data=fixture();data['nodes'][0]['invert']=None
+        self.assertEqual(self.run_case(data)['status'],'failed')
+
+    def test_duplicate_inp_id_is_caught(self):
+        text=INP+'A 5 6\n'
+        self.assertEqual(self.run_case(fixture(text),text)['status'],'failed')
+
+    def test_source_hash_is_checked(self):
+        data=fixture();data['meta']['sha256']='wrong'
+        self.assertEqual(self.run_case(data)['status'],'failed')
+
+    def test_elevation_offsets_are_absolute(self):
+        text=INP.replace('LINK_OFFSETS DEPTH','LINK_OFFSETS ELEVATION')
+        data=fixture(text);data['meta']['offsetMode']='ELEVATION'
+        data['links'][0].update(invertStart=.2,invertEnd=.1,centerStart=.5,centerEnd=.4)
+        data['links'][0].update(slopeInput=.02,slopePlan=.02)
+        self.assertEqual(self.run_case(data,text)['status'],'passed')
+
+    def test_rectangular_width_and_height_are_distinct(self):
+        text=INP.replace('P CIRCULAR 0.6 0 0 0 1','P RECT_CLOSED 0.6 1.2 0 0 1')
+        data=fixture(text)
+        data['links'][0]['section'].update(shape='RECT_CLOSED',width=1.2,diameter=None,
+                                         raw='P RECT_CLOSED 0.6 1.2 0 0 1'.split())
+        data['summary']['shapes']={'RECT_CLOSED':1}
+        self.assertEqual(self.run_case(data,text)['status'],'passed')
+        data['links'][0]['section']['width']=.6
+        self.assertEqual(self.run_case(data,text)['status'],'failed')
+
+    def test_missing_coordinate_requires_documented_exclusion(self):
+        text=INP.replace('B 3 4\n','')
+        data=fixture(text);data['nodes'][1]['xy']=None
+        data['links'][0].update(pathXY=None,planDistance=None,renderable=False,
+                               lengthDelta=None,lengthDifferenceRatio=None,slopePlan=None)
+        data['summary']['coordinateCount']=1
+        data['summary']['renderedConduits']=0
+        self.assertEqual(self.run_case(data,text)['status'],'failed')
+        data['issues']=[{'code':'missing_coordinate','ids':['B']},{'code':'unplaced_link','ids':['P']}]
+        self.assertEqual(self.run_case(data,text)['status'],'passed')
+
+    def test_unsupported_shape_does_not_pass(self):
+        text=INP.replace('CIRCULAR','CUSTOM')
+        with self.assertRaisesRegex(ValueError,'unsupported conduit shape'):
+            self.run_case(fixture(text),text)
+
+
+if __name__=='__main__':
+    unittest.main()