Add doctest for issue #37417

Author: GiacomoPope

src/sage/schemes/elliptic_curves/cm.py

@@ -233,6 +233,13 @@ def is_HCP(f, check_monic_irreducible=True):
         sage: all(not is_HCP(hilbert_class_polynomial(D) + 1)
         ....:     for D in srange(-4,-100,-1) if D.is_discriminant())
         True
+
+    Ensure that :issue:`37471` is fixed::
+
+        from sage.schemes.elliptic_curves.cm import is_HCP
+        set_random_seed(297388353221545796156853787333338705098)
+        is_HCP(hilbert_class_polynomial(-55))
+        -55
     """
     zero = ZZ(0)
     # optional check that input is monic and irreducible