Health checks

Hypothesis tries to detect common mistakes and things that will cause difficulty at run time in the form of a number of ‘health checks’.

These include detecting and warning about:

• Strategies with very slow data generation
• Strategies which filter out too much
• Recursive strategies which branch too much
• Tests that are unlikely to complete in a reasonable amount of time.

If any of these scenarios are detected, Hypothesis will emit a warning about them.

The general goal of these health checks is to warn you about things that you are doing that might appear to work but will either cause Hypothesis to not work correctly or to perform badly.

To selectively disable health checks, use the suppress_health_check setting. The argument for this parameter is a list with elements drawn from any of the class-level attributes of the HealthCheck class. Using a value of HealthCheck.all() will disable all health checks.

class hypothesis.HealthCheck

Arguments for suppress_health_check.

Each member of this enum is a type of health check to suppress.

data_too_large = 1

Check for when the typical size of the examples you are generating exceeds the maximum allowed size too often.

filter_too_much = 2

Check for when the test is filtering out too many examples, either through use of assume() or filter(), or occasionally for Hypothesis internal reasons.

too_slow = 3

Check for when your data generation is extremely slow and likely to hurt testing.

return_value = 5

Checks if your tests return a non-None value (which will be ignored and is unlikely to do what you want).

hung_test = 6

This health check is deprecated and no longer has any effect. You can use the max_examples and deadline settings together to cap the total runtime of your tests, rather than the previous fixed limit.

large_base_example = 7

Checks if the natural example to shrink towards is very large.

not_a_test_method = 8

Checks if @given has been applied to a method defined by unittest.TestCase (i.e. not a test).

Deprecations

We also use a range of custom exception and warning types, so you can see exactly where an error came from - or turn only our warnings into errors.

class hypothesis.errors.HypothesisDeprecationWarning

A deprecation warning issued by Hypothesis.

Actually inherits from FutureWarning, because DeprecationWarning is hidden by the default warnings filter.

You can configure the Python warnings to handle these warnings differently to others, either turning them into errors or suppressing them entirely. Obviously we would prefer the former!

Deprecated features will be continue to emit warnings for at least six months, and then be removed in the following major release. Note however that not all warnings are subject to this grace period; sometimes we strengthen validation by adding a warning and these may become errors immediately at a major release.