Programming language: Kotlin
License: MIT License
Tags: Tests    
Latest version: v0.1.0-beta

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Build Status codecov

⚠️ Release status

This library is in a "proof of concept" stage:

  • the API is unstable and may change in a non-backward-compatible way,
  • it's hard to write the tests, it requires creating the visualization column by column
  • failed assertions produce messages that are hard to relate to the function
  • it contains several known bugs

Feel free to experiment with it, but avoid using in production.

What is PlotAssert?

It's a Kotlin library to write visually appealing ASCII-art-like test assertions for math functions. For example, you can test that your (Float) -> Float function describing a sine wave produces proper values. Or if you have a game where the player jumps, you can describe player's vertical position as a function of time - you could test this function to make sure that the jump movement is fluent and fast enough.

Under the hood, each such ASCII visualisation is translated into a collection of constraints, where each constraint looks at a single X value of the function and performs a certain check on its Y value at this point.


In your build.gradle:

repositories {
    maven {
        url "https://dl.bintray.com/krzema1212/it.krzeminski"

dependencies {
    testCompile "it.krzeminski:PlotAssert:0.1.0-beta"


fun sineWaveFor2HzOnePeriod() {
            functionUnderTest = sineWave(frequency = 2.0f),
            visualisation = {
                row(1.0f,   "        IIXII                            ")
                row(        "     III     III                         ")
                row(        "    I           I                        ")
                row(        "  II             II                      ")
                row(        " I                 I                     ")
                row(0.0f,   "X                   I                   I")
                row(        "                     I                 I ")
                row(        "                      II             II  ")
                row(        "                        I           I    ")
                row(        "                         III     III     ")
                row(-1.0f,  "                            IIIII        ")
                xAxis {
                    markers("|                   |                   |")
                    values( 0.0f,               0.25f,              0.5f)

or for high-frequency function and higher sampling:

fun assertFunctionConformsToForHighFrequencyFunctionWhenAssertionsAreFulfilledAndSamplingHigherThan1IsUsed() {
        functionUnderTest = { x: Float -> (sin(100*x) * sin(x) * x * 0.3).toFloat() },
        samplesPerCharacter = 100,
        visualisation = {
            row( 2.0f,  "                                                                   ")
            row(        "                                                                   ")
            row(        "                                               IIIIIIIIIIIIII      ")
            row( 1.0f,  "                                           IIIIIIIIIIIIIIIIIIIII   ")
            row(        "                   IIIIIIII             IIIIIIIIIIIIIIIIIIIIIIIIIII")
            row(        "                  IIIIIIII              IIIIIIIIIIIIIIIIIIIIIIIIIII")
            row(-1.0f,  "                                            IIIIIIIIIIIIIIIIIIII   ")
            row(        "                                               IIIIIIIIIIIIII      ")
            row(        "                                                                   ")
            row(-2.0f,  "                                                                   ")
            xAxis {
                markers("|          |          |          |          |          |          |")
                values( 0.0f,      1.0f,      2.0f,      3.0f,      4.0f,      5.0f,      6.0f)


  • I characters mean that for a given X argument, the function's value can be in a certain range around a given Y value. Also, this constraint is "strict", which means that making it wider or narrower vertically would make the assertion fail. In this example, each I character has a tolerance of +/- 0.1. The tolerance is calculated based on the vertical axis description.
  • X characters mean that for a given X argument, the function's value has to exactly match the given Y value.

There's also i constraint, which just checks that all values are in a certain range.

More examples can be found in unit tests for krzema12/fsynth - a project that PlotAssert was created for.


  • the library performs sampling, as given by the xAxis description and samplesPerCharacter parameter. It means that if two subsequent X values are 0.2 and 0.3, and not enough sampling rate is given, the library may not check what happens for 0.25 or 0.20001. In most cases, such simple sampling is enough.
  • only (Float) -> Float functions are currently supported. Mitigation: it's possible to assert on any other function, as long as it can be presented as a (Float) -> Float function. See this example for adapting an (Int) -> Float function
  • when assertions fail, the current message just says about failed first (x, y) constraint, going from the left. It's thus quite time-consuming to write a test. Ideally, if the assertion fails, PlotAssert should show how the ASCII visualisation could look like.