Fake-O-Matic

Fake-O-Matic is a utility tool for creating fake data.

How to Configure

Fake-O-Matic is configured through a set of yaml files that forms a hierarchy. If some configuration is not found on one file, then the next file is used. That also means that you can override configurations by leaving the default values as the last in the hierarchy.

A Fake-O-Matic configuration has:

samples: # (1)
  sample_name:
    # configuration

placeholders: # (2)
  "PLACEHOLDER_CHARACTER": sample_name

1. Ideally as many samples as needed

2. Optional placeholders for creating expressions

The configuration for each part is covered through this document.

Configuration Values

Some configuration values can be externalized by different ways additionally to the normal String value:

env

Fetches the value from an Environment Variable.

param:
  env: PARAM # reads the value from the PARAM environment variable (export PARAM=foo)

property

Fetches the value from a System Property.

param:
  property: my.parameter # reads the value from the my.parameter system property (-Dmy.parameter=foo)

file

Reads the value from a file.

param:
  file: /tmp/myfile # reads the value from the /tmp/myfile content

resource

Reads the value using a class.getResourceAsStream.

param:
  resource: /com/example/configuration.yaml # reads the value from the configuration.yaml
                                            # file inside the com.example package

url

Reads the value from the given URL by using GET url.

param:
  url: https://something.example.com/some-param

value

Supplies a raw value.

param:
  value: bar # uses "bar" as the value if the PARAM environment variable is not present

It is also possible to combine different approaches for getting the value by passing all the desired options. The first one that holds a value will be used (see the priority bellow):

param:
  env: PARAM
  property: my.parameter
  value: bar

The priority for getting the value is:

1. env

2. property

3. file

4. resource

5. url

6. value

It’s also possible to supply a raw value without specifying the type value if it’s the only value:

param: some value # implies a configuration of type "value"

Sample as Configuration

Some samples take other samples as configuration. In most cases, there are two ways of passing a sample as configuration:

1. Referring through a ref property.

2. Directly through a sample property.

Data Generation

The rules for generating data can contain sample and placeholders. Samples are a set of data that Fake-O-Matic can randomly pick and placeholders are characters that can be associated with the samples for to allow the use of expressions for generating data.

Samples

Characters

This sample can pick any character from a given string. Useful for defining a set of characters that can be used to produce IDs or any other information that is not meant to be read.

Configuration

type

chars

value

String that holds the chars

Example

samples:
  letter:
    type: chars
    value: "abcdefghijklmnopqrstuvwxyz"
  digit:
    type: chars
    value: "0123456789"

List

This sample can pick any item from a given list of objects.

Configuration

type

list

values

List of raw values to use.

samples

List of Samples to use.

source

A configuration pointing to where to locate the list of values.

Note	You need to supply only one way of loading the values (values, sample or source).

Example

samples:
  cause:
    type: list
    values:
      - "clock speed"
      - "solar flares"
      - "electromagnetic radiation from satellite debris"
      - "static from nylon underwear"
      - "static from plastic slide rules"
      - "global warming"
      - "poor power conditioning"
      - "static buildup"
      - "doppler effect"
  first_name:
    type: list
    samples:
      - man_name
      - woman_name
  story:
    type: list
    source:
      env: STORIES
      property: stories
      default: stories.txt

API

This sample actually calls a given API to get data to use every time it’s asked for a data.

Warning

Due to the nature of this sample, it’s not possible to reproduce the same payloads without relying on the dependent API.

Configuration

JSON Pointer

This sample extracts a value from a JSON object. Useful when used in combination with the API Sample.

Configuration

type

json

path

A JSON Pointer to specify which value to take from the JSON object.

source

Which sample sample should be used to obtain the JSON object.

Example

samples:
  whatthecommit:
    type: http
    url: https://whatthecommit.com/index.txt

Universally Unique Identifier

This sample will produce a universally unique identifier.

Configuration

type

uuid

Example

samples:
  uuid:
    type: uuid

Join

This sample will gather other samples and join them into one data.

Configuration

type

join

samples

Which samples to join

separator

Which separator to use (defaults to an empty string).

Example

samples:
  full_name:
    type: join
    separator: " "
    samples:
      - first_name
      - last_name

Weight

A sample that allows you to define specific weights to each element.

Configuration

type

weight

values

The list of values.

weight

The weight of the value.

value

The value to use.

source

Which sample sample should be used instead of the value.

Example

samples:
  color:
    type: weight
    values:
      - weight: 30
        value: blue
      - weight: 45
        value: yellow
      - weight: 10
        value: red
      - weight: 20
        value: brown
      - weight: 25
        value: cyan

Note	The sum of the weights don’t necessary need to be 100, but using a total weight of 100 helps to see the weights as percentage.

Range

This sample generates numbers from a given interval.

Configuration

type

range

min

The minimum value.

max

The maximum value.

Example

samples:
  grade:
    type: range
    min: 0
    max: 10
  temperature:
    type: range
    min: -10
    max: 20

Expression

A sample that generates data based on expressions.

Configuration

type

expression

sample

The sample to use as an expression.

expression

The expression to use.

Note	You need to supply a sample or an expression.

Example

samples:
  address_expression:
    type: list
    values:
      - "Some Street ##"
      - "Another Street ###"
      - "Galaxy ###"
  address:
    type: expression
    sample: address_expression
  credit_card:
    type: expression
    expression: "################"

Date

A sample that can generate dates based on a given interval.

Configuration

type

date

from

Defines the start date.

to

Defines the end date.

period

Defines a period instead of an end date. See the docs for java.time.Period#parse.

format

The format to parse the supplied dates. Defaults to dd-MM-yyyy. See the docs for java.time.format.DateTimeFormatter#ofPatter.

inclusive

Sets if the end date is part of the interval or not.

Note	It is possible to use today, yesterday or tomorrow instead of the actual date values.

Example

samples:
  day_in_2020:
    type: date
    from: 2020-01-01
    to: 2021-01-01
  day_in_quarter:
    type: date
    from: 2020-01-01
    period: P3M
  yesterday_to_tomorrow:
    type: date
    from: yesterday
    to: tomorrow
    inclusive: true

Cache

A sample that caches the value. Useful when used with an API sample that posts data in order to create a data dependency.

Configuration

type

cache

source

Which sample sample should be used to obtain the value to cache.

ttl

How many hits the value should last until the cache gets another one. This is a configuration value.

Example

samples:
  new_person:
    type: api
    url: http://api.example.com/persons
    method: POST
    payload:
      template: person.json
    return: /id
  person:
    type: cache
    source:
      ref: new_person

Placeholders

The placeholders are a single character that can be associated with any of the configured sample. Bellow is an example of a configuration file:

placeholders:
  "#": digit   (1)
  "%": letter  (2)

samples:
  letter:
    type: chars
    value: "abcdefghijklmnopqrstuvwxyz"
  digit:
    type: chars
    value: "0123456789"

1. Associated with the digit sample

2. Associated with the letter sample

Payload Template

Fake-O-Matic uses Qute templates to produce the payloads. A couple of methods can be used to get a fake data, the main one are:

some(sampleName)

Gets a random sample from the given sample name.

expression(placeholders)

Gets a random data produced by replacing each placeholder by a random sample associated with it.

Configuration Properties

The following properties can be configured as a JVM argument (prefix -D), environment variable (with upper cases and underscores), or a command line parameter:

generator.total|GENERATOR_TOTAL|--total

The number of generated payloads. Defaults to 10.

generator.config|GENERATOR_CONFIG|--config

Which configuration files should be used. Fake-O-Matic allows you to define parent configurations, so you can reuse them in the way it suits you better. The configurations should be comma separated from the most specific to the least specific (so the last configuration file becomes the parent one). The built-in configuration can be included with a simple fakeomatic name. The built-in configuration can be found at src/main/resources/META-INF/config/fakeomatic.yaml.

Note	The --config param can be also used once for each file to include.

generator.seed|GENERATOR_SEED|--seed

The seed to use for the random functions. Fake-O-Matic will generate one if empty.

fakeomatic.events.log.level|FAKEOMATIC_EVENTS_LOG_LEVEL|--events-log-level

Sets the log level for the events. To see all the payloads and responses, set the log level to DEBUG.

Example

The following examples can be used with the built-in configuration.

{
  "id": "{some('uuid')}",
  "cause": "{some('error_cause')}",
  "device": "{expression('%%-#####')}"
}

{
  "level": "{oneOf('INFO', 'WARN', 'ERROR')}",
  "message": "{some('business_bullshit')}"
}