sage.numerical.backends: GenericBackend doctests failure in remove_constraints

[yzh]

Although the doctests in generic_backend are purely decoration (disabled using optional - Nonexistent_LP_solver), they provide template for copy paste to other backends. The following doctest from the method GenericBackend.remove_constraints fails, because the backend p does not have the methods new_variable and add_constraints. (These are methods of MixedIntegerLinearProgram.)

sage: from sage.numerical.backends.generic_backend import get_solver
sage: p = get_solver(solver = "Nonexistent_LP_solver")  # optional - Nonexistent_LP_solver
sage: p.add_constraint(p[0] + p[1], max = 10)           # optional - Nonexistent_LP_solver
sage: p.remove_constraints([0])                         # optional - Nonexistent_LP_solver

[yzh]

Notice that @classmethod _test_remove_constraint and _test_remove_constraints are missing. They should be added to generic_backend_test.py in #31103 later.

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New commits:

​6a93d7e

fix doctest

[mkoeppe]

Are there copies of this test template in the backends that are correct?

[yzh]

Replying to mkoeppe:

Are there copies of this test template in the backends that are correct?

This method is not defined in most backends. Only glpk_backend.pyx has it. The test there is correct, but it uses p = MixedIntegerLinearProgram(...) instead.