Add test for suicide prereqs

tests/integration/test_remove.py

@@ -340,3 +340,34 @@ async def test_prereqs(
         ('1/a2', None),
         ('1/b', None),
     }
+
+
+async def test_suicide(flow, scheduler, run, reflog, complete):
+    """Test that suicide prereqs are unset by `cylc remove`."""
+    schd: Scheduler = scheduler(
+        flow({
+            'scheduling': {
+                'graph': {
+                    'R1': '''
+                        a => b => c => d => x
+                        a & c => !x
+                    '''
+                },
+            },
+        }),
+        paused_start=False,
+    )
+    async with run(schd):
+        reflog_triggers: set = reflog(schd)
+        await complete(schd, '1/b')
+        await run_cmd(remove_tasks(schd, ['1/a'], [FLOW_ALL]))
+        await complete(schd)
+
+    assert reflog_triggers == {
+        ('1/a', None),
+        ('1/b', ('1/a',)),
+        ('1/c', ('1/b',)),
+        ('1/d', ('1/c',)),
+        # 1/x not suicided as 1/a was removed:
+        ('1/x', ('1/d',)),
+    }