Runtime testing - The Turing Way

Runtime tests are tests that run as part of the program itself. They may take the form of checks within the code, as shown below:

population = population + people_born - people_died

// test that the population is positive
if (population < 0):
  error( 'The number of people can never be negative' )

Another example of a use of runtime tests is internal checks within functions that verify that their inputs and outputs are valid, as shown below:

function add_arrays( array1, array2 ):

// test that the arrays have the same size
if (array1.size() != array2.size()):
  error( 'The arrays have different sizes!' )

output = array1 + array2

if (output.size() != array1.size()):
  error( 'The output array has the wrong size!'' )

return output

Advantages of runtime testing:

Run within the program, so can catch problems caused by logic errors or edge cases.
Makes it easier to find the cause of the bug by catching problems early.
Catching problems early also helps prevent them escalating into catastrophic failures. It minimises the blast radius.

Disadvantages of runtime testing:

Tests can slow down the program.
What is the right thing to do if an error is detected? How should this error be reported? Exceptions are a recommended route to go with this.