Unit Test Common Runtime Parameters

There are a number of runtime parameters that are common to all (or most) of the unit tests. These are defined in the top-level unit_test/_parameters file.

Thermodynamics

The equation of state enforces minimum density and temperatures, which must be set upon initialization. These are controlled by the following runtime parameters:

unit_test.small_temp : the low temperature cutoff used in the equation of state
unit_test.small_dens : the low density cutoff used in the equation of state

Defining composition

Most of the unit tests require a composition to be defined (for the initial mass-fractions, $X_{k}$ ). There are a few ways this can be done (depending on the test).

One-zone (*_cell) tests (see One Zone Tests) usually do one of:
- Explicitly setting the individual mass fractions. This is controlled by the parameters unit_test.X1, unit_test.X2, …, unit_test.X35, e.g.:
```
unit_test.X1 = 0.5
unit_test.X2 = 0.2
unit_test.X3 = 0.2
unit_test.X4 = 0.1
```
  While many of the tests will renormalize the abundances, the user should take care to ensure that the mass fractions sum to unity.
- Setting the composition to be uniform. This is controlled by unit_test.uniform_xn. If this is set to 1, then each mass fraction is initialized to 1 / NumSpec.
Comprehensive tests (see Comprehensive Unit Tests) need many different compositions, since they are creating a cube

of varying thermodynamic properties, and thus require a prescription to create the composition. This is done by setting unit_test.primary_species_1, unit_test.primary_species_2, and unit_test.primary_species_3 to one of the names of the species in the network.

The function setup_composition() is then used to set limits on the species abundances (it takes a parameter which is the index into the cube of data that is being initialized) which is then used by get_xn() to create the individual mass fractions. Both of these routines are contained in react_util.H.