# Tests¶

## Convergence test¶

The `test-convergence.py`

script solves for the same plasma as the
`01-freeboundary.py`

example, with four poloidal field coils and an X-point.
The change in results as the resolution is doubled is plotted as a function of
grid resolution. This is therefore not testing convergence to a known solution,
but is a check that the code converges to value, and indication of its
convergence rate.
Results are shown below, using the von Hagenow free boundary, and 4th-order solver for
the poloidal flux .

This indicates that in general convergence is between 2nd and 4th-order. The plasma volume is currently calculated by integrating over the poloidal cross-section, and could be improved by converting this to a surface integral.