Assertions Premium/Enterprise

An assertion is an expression that must return a Boolean (true if the assertion succeeds, false otherwise).

It always relies on metric values, operators, units, functions, and variables and must be written in the tests section of the .blackfire.yaml file:

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tests:
    'All pages are fast':
        path: '/.*'
        assertions:
            - 'main.wall_time < 50ms'
            - 'main.peak_memory < 10mb'
            - 'main.network_out < 10kb'

    'Not too many SQL queries on the homepage':
        path: '/(en|fr)/blog/'
        assertions:
            - 'metrics.sql.queries.count < 5'

In the above example, main.network_out, metrics.sql.queries.count, and main.peak_memory are metric values. Unit like in 10mb can be explicit in order to override default units.

Note

Whenever possible, we recommend you write assertions that do not depend on time. The main reason is that time is always a consequence, a symptom of a deeper issue.

Comparison Assertions

Assertions support profile comparison as well to assert the performance evolution of your code:

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tests:
    "Pages should not become slower":
        path: "/.*"
        assertions:
            - "percent(main.wall_time) < 10%"       # time does not increase by more than 10%
            - "diff(metrics.sql.queries.count) < 2" # less than 2 additional SQL statements

Note

Comparison assertions are only evaluated when running builds.

Values are compared between the current build and a reference build. The reference can be either the last successful periodic build, or a build that has been referenced in the webhook command with --external_parent_id option.

Metric Values

Blackfire exposes metrics that are associated with the current profile. The value of one dimension of a metric can be used in assertions; for instance, the count value of the sql.queries metric is stored in metrics.sql.queries.count.

Learn more about all built-in metrics exposed in assertions by default and how to create your own.

The available dimensions for metrics are the following ones:

  • count
  • wall_time
  • cpu_time
  • memory
  • peak_memory
  • network_in
  • network_out
  • io

Units

For each metric (count, time or memory), a default unit is defined:

  • The default time unit is the millisecond;
  • The default memory unit is the byte.

When using 10 in an assertion for a time value, that evaluates to 10 milliseconds. It is possible to add an explicit unit to a metric, which will override the default unit.

The following time units are supported: ms, s.

The following memory units are supported: kb, kib, mb, mib, gb, gib.

The following generic units are supported: k, ki, m, mi, g, gi.

Operators

The following operators are supported in assertions:

Comparison

  • == equals;
  • != not equals;
  • < less than;
  • > greater than;
  • <= less than or equal to;
  • >= greater than or equal to.

Logic

  • not or !;
  • and or &&;
  • or or ||.

Math

  • + addition;
  • - subtraction;
  • * multiplication;
  • / division;
  • % modulus;
  • ** pow.

Variables

Variables are useful when you configure several Blackfire environments to run performance tests on various machines hosting the same application. Variables make it possible to use the same .blackfire.yaml configuration on several servers that have different purposes (e.g. development, staging, production).

Variables can be defined in the environment configuration and used in an expression by passing the metric key to the var() function. Variable values may also use units.

Example: You have configured two different environments in Blackfire:

  • Integration hits your integration server, where your application runs with debug mode on;
  • Production hits your production servers, where your application runs with debug mode off.

The same application runs on all servers, but the debug mode increases memory usage a lot. As such, you cannot set the same maximum value for your assertions on memory.

Your .blackfire.yaml would look like this when using variables:

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tests:
    "Pages shouldn't use too much memory":
        path: "/.*"
        assertions:
            - "main.peak_memory < 10mb * var('memory_coeff')"

Now in both your Integration and Production Blackfire environments, you have to create the memory_coeff variable:

  • For Integration, memory_coeff == 2
  • For Production, memory_coeff == 1

The var() function may also receive a default value as a second argument. This default value is used whenever the variable is not defined in one of your environments.

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tests:
    "Pages shouldn't use too much memory":
        path: "/.*"
        assertions:
            - "main.peak_memory < 10mb * var('memory_coeff', 1)"

Caution

The vars.xxx notation, supported in older versions of Blackfire, is now deprecated. We strongly advise you to migrate your expression to use the var() function instead.

Development vs Production

When an assertion is run from an environment, the is_dev() function returns false when the environment is configured for production usage.

Builds Comparison

When using builds, it is possible to compare one build to another. This is useful when you want to validate a code merge (e.g. a pull-request) by triggering a build webhook or a Blackfire Player collection of scenarios. It can also ensure that your code doesn’t have performance regression over time using periodic builds.

Comparison can be made within assertion expressions thanks to the percent() and diff() functions:

If you want to assert that a metric value does not increase by more than a given percentage between two builds, use the percent() function:

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"percent(main.wall_time) < 10%"

You can also test the evolution of a metric value in absolute terms with the diff() function:

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"diff(metrics.sql.queries.count) < 2"

In this example, the assertion checks that the profile from the newer build has less than 2 additional SQL statements compared to the previous one.