path: root/layout/style/test/flexbox_layout_testcases.js

/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* vim: set ts=2 sw=2 sts=2 et: */

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * For the purposes of this test, flex items are specified as a hash with a
 * hash-entry for each CSS property that is to be set.  In these per-property
 * entries, the key is the property-name, and the value can be either of the
 * following:
 *  (a) the property's specified value (which indicates that we don't need to
 *      bother checking the computed value of this particular property)
 *  ...OR...
 *  (b) an array with 2-3 entries...
 *        [specifiedValue, expectedComputedValue (, epsilon) ]
 *      ...which indicates that the property's computed value should be
 *      checked.  The array's first entry (for the specified value) may be
 *      null; this means that no value should be explicitly specified for this
 *      property. The second entry is the property's expected computed
 *      value. The third (optional) entry is an epsilon value, which allows for
 *      fuzzy equality when testing the computed value.
 *
 * To allow these testcases to be re-used in both horizontal and vertical
 * flex containers, we specify "width"/"min-width"/etc. using the aliases
 * "_main-size", "_min-main-size", etc.  The test code can map these
 * placeholder names to their corresponding property-names using the maps
 * defined below -- gRowPropertyMapping, gColumnPropertyMapping, etc.
 *
 * If the testcase needs to customize its flex container at all (e.g. by
 * specifying a custom container-size), it can do so by including a hash
 * called "container_properties", with propertyName:propertyValue mappings.
 * (This hash can use aliased property-names like "_main-size" as well.)
 */

// The standard main-size we'll use for our flex container when setting up
// the testcases defined below:
var gDefaultFlexContainerSize = "200px";

// Left-to-right versions of placeholder property-names used in
// testcases below:
var gRowPropertyMapping = {
  "_main-size": "width",
  "_min-main-size": "min-width",
  "_max-main-size": "max-width",
  "_border-main-start-width": "border-left-width",
  "_border-main-end-width": "border-right-width",
  "_padding-main-start": "padding-left",
  "_padding-main-end": "padding-right",
  "_margin-main-start": "margin-left",
  "_margin-main-end": "margin-right",
};

// Right-to-left versions of placeholder property-names used in
// testcases below:
var gRowReversePropertyMapping = {
  "_main-size": "width",
  "_min-main-size": "min-width",
  "_max-main-size": "max-width",
  "_border-main-start-width": "border-right-width",
  "_border-main-end-width": "border-left-width",
  "_padding-main-start": "padding-right",
  "_padding-main-end": "padding-left",
  "_margin-main-start": "margin-right",
  "_margin-main-end": "margin-left",
};

// Top-to-bottom versions of placeholder property-names used in
// testcases below:
var gColumnPropertyMapping = {
  "_main-size": "height",
  "_min-main-size": "min-height",
  "_max-main-size": "max-height",
  "_border-main-start-width": "border-top-width",
  "_border-main-end-width": "border-bottom-width",
  "_padding-main-start": "padding-top",
  "_padding-main-end": "padding-bottom",
  "_margin-main-start": "margin-top",
  "_margin-main-end": "margin-bottom",
};

// Bottom-to-top versions of placeholder property-names used in
// testcases below:
var gColumnReversePropertyMapping = {
  "_main-size": "height",
  "_min-main-size": "min-height",
  "_max-main-size": "max-height",
  "_border-main-start-width": "border-bottom-width",
  "_border-main-end-width": "border-top-width",
  "_padding-main-start": "padding-bottom",
  "_padding-main-end": "padding-top",
  "_margin-main-start": "margin-bottom",
  "_margin-main-end": "margin-top",
};

// The list of actual testcase definitions:
var gFlexboxTestcases = [
  // No flex properties specified --> should just use 'width' for sizing
  {
    items: [
      { "_main-size": ["40px", "40px"] },
      { "_main-size": ["65px", "65px"] },
    ],
  },
  // flex-basis is specified:
  {
    items: [
      { "flex-basis": "50px", "_main-size": [null, "50px"] },
      {
        "flex-basis": "20px",
        "_main-size": [null, "20px"],
      },
    ],
  },
  // flex-basis is *large* -- sum of flex-basis values is > flex container size:
  // (w/ 0 flex-shrink so we don't shrink):
  {
    items: [
      {
        flex: "0 0 150px",
        "_main-size": [null, "150px"],
      },
      {
        flex: "0 0 90px",
        "_main-size": [null, "90px"],
      },
    ],
  },
  // flex-basis is *large* -- each flex-basis value is > flex container size:
  // (w/ 0 flex-shrink so we don't shrink):
  {
    items: [
      {
        flex: "0 0 250px",
        "_main-size": [null, "250px"],
      },
      {
        flex: "0 0 400px",
        "_main-size": [null, "400px"],
      },
    ],
  },
  // flex-basis has percentage value:
  {
    items: [
      {
        "flex-basis": "30%",
        "_main-size": [null, "60px"],
      },
      {
        "flex-basis": "45%",
        "_main-size": [null, "90px"],
      },
    ],
  },
  // flex-basis has calc(percentage) value:
  {
    items: [
      {
        "flex-basis": "calc(20%)",
        "_main-size": [null, "40px"],
      },
      {
        "flex-basis": "calc(80%)",
        "_main-size": [null, "160px"],
      },
    ],
  },
  // flex-basis has calc(percentage +/- length) value:
  {
    items: [
      {
        "flex-basis": "calc(10px + 20%)",
        "_main-size": [null, "50px"],
      },
      {
        "flex-basis": "calc(60% - 1px)",
        "_main-size": [null, "119px"],
      },
    ],
  },
  // flex-grow is specified:
  {
    items: [
      {
        flex: "1",
        "_main-size": [null, "60px"],
      },
      {
        flex: "2",
        "_main-size": [null, "120px"],
      },
      {
        flex: "0 20px",
        "_main-size": [null, "20px"],
      },
    ],
  },
  // Same ratio as prev. testcase; making sure we handle float inaccuracy
  {
    items: [
      {
        flex: "100000",
        "_main-size": [null, "60px"],
      },
      {
        flex: "200000",
        "_main-size": [null, "120px"],
      },
      {
        flex: "0.000001 20px",
        "_main-size": [null, "20px"],
      },
    ],
  },
  // Same ratio as prev. testcase, but with items cycled and w/
  // "flex: none" & explicit size instead of "flex: 0 20px"
  {
    items: [
      {
        flex: "none",
        "_main-size": ["20px", "20px"],
      },
      {
        flex: "1",
        "_main-size": [null, "60px"],
      },
      {
        flex: "2",
        "_main-size": [null, "120px"],
      },
    ],
  },

  // ...and now with flex-grow:[huge] to be sure we handle infinite float values
  // gracefully.
  {
    items: [
      {
        flex: "9999999999999999999999999999999999999999999999999999999",
        "_main-size": [null, "200px"],
      },
    ],
  },
  {
    items: [
      {
        flex: "9999999999999999999999999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "9999999999999999999999999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "9999999999999999999999999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "9999999999999999999999999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
    ],
  },
  {
    items: [
      {
        flex: "99999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "99999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "99999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
      {
        flex: "99999999999999999999999999999999999",
        "_main-size": [null, "50px"],
      },
    ],
  },

  // And now, some testcases to check that we handle float accumulation error
  // gracefully.

  // First, a testcase with just a custom-sized huge container, to be sure we'll
  // be able to handle content on that scale, in the subsequent more-complex
  // testcases:
  {
    container_properties: {
      "_main-size": "9000000px",
    },
    items: [
      {
        flex: "1",
        "_main-size": [null, "9000000px"],
      },
    ],
  },
  // ...and now with two flex items dividing up that container's huge size:
  {
    container_properties: {
      "_main-size": "9000000px",
    },
    items: [
      {
        flex: "2",
        "_main-size": [null, "6000000px"],
      },
      {
        flex: "1",
        "_main-size": [null, "3000000px"],
      },
    ],
  },

  // OK, now to actually test accumulation error. Below, we have six flex items
  // splitting up the container's size, with huge differences between flex
  // weights.  For simplicity, I've set up the weights so that they sum exactly
  // to the container's size in px. So 1 unit of flex *should* get you 1px.
  //
  // NOTE: The expected computed "_main-size" values for the flex items below
  // appear to add up to more than their container's size, which would suggest
  // that they overflow their container unnecessarily. But they don't actually
  // overflow -- this discrepancy is simply because Gecko's code for reporting
  // computed-sizes rounds to 6 significant figures (in particular, the method
  // (nsTSubstring_CharT::AppendFloat() does this).  Internally, in app-units,
  // the child frames' main-sizes add up exactly to the container's main-size,
  // as you'd hope & expect.
  {
    container_properties: {
      "_main-size": "9000000px",
    },
    items: [
      {
        flex: "3000000",
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "1",
        "_main-size": [null, "1px"],
      },
      {
        flex: "1",
        "_main-size": [null, "1px"],
      },
      {
        flex: "2999999",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "2999998",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "1",
        "_main-size": [null, "1px", 0.2],
      },
    ],
  },
  // Same flex items as previous testcase, but now reordered such that the items
  // with tiny flex weights are all listed last:
  {
    container_properties: {
      "_main-size": "9000000px",
    },
    items: [
      {
        flex: "3000000",
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "2999999",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "2999998",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "1",
        "_main-size": [null, "1px", 0.2],
      },
      {
        flex: "1",
        "_main-size": [null, "1px", 0.2],
      },
      {
        flex: "1",
        "_main-size": [null, "1px", 0.2],
      },
    ],
  },
  // Same flex items as previous testcase, but now reordered such that the items
  // with tiny flex weights are all listed first:
  {
    container_properties: {
      "_main-size": "9000000px",
    },
    items: [
      {
        flex: "1",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths:
        "_main-size": [null, "1px", 0.2],
      },
      {
        flex: "1",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths:
        "_main-size": [null, "1px", 0.2],
      },
      {
        flex: "1",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths:
        "_main-size": [null, "1px", 0.2],
      },
      {
        flex: "3000000",
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "2999999",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
      {
        flex: "2999998",
        // NOTE: Expected value is off slightly, from float error when
        // resolving flexible lengths & when generating computed value string:
        "_main-size": [null, "3000000px"],
      },
    ],
  },

  // Trying "flex: auto" (== "1 1 auto") w/ a mix of flex-grow/flex-basis values
  {
    items: [
      {
        flex: "auto",
        "_main-size": [null, "45px"],
      },
      {
        flex: "2",
        "_main-size": [null, "90px"],
      },
      {
        flex: "20px 1 0",
        "_main-size": [null, "65px"],
      },
    ],
  },
  // Same as previous, but with items cycled & different syntax
  {
    items: [
      {
        flex: "20px",
        "_main-size": [null, "65px"],
      },
      {
        flex: "1",
        "_main-size": [null, "45px"],
      },
      {
        flex: "2",
        "_main-size": [null, "90px"],
      },
    ],
  },
  {
    items: [
      {
        flex: "2",
        "_main-size": [null, "100px"],
        border: "0px dashed",
        "_border-main-start-width": ["5px", "5px"],
        "_border-main-end-width": ["15px", "15px"],
        "_margin-main-start": ["22px", "22px"],
        "_margin-main-end": ["8px", "8px"],
      },
      {
        flex: "1",
        "_main-size": [null, "50px"],
        "_margin-main-start": ["auto", "0px"],
        "_padding-main-end": ["auto", "0px"],
      },
    ],
  },
  // Test negative flexibility:

  // Basic testcase: just 1 item (relying on initial "flex-shrink: 1") --
  // should shrink to container size.
  {
    items: [{ "_main-size": ["400px", "200px"] }],
  },
  // ...and now with a "flex" specification and a different flex-shrink value:
  {
    items: [
      {
        flex: "4 2 250px",
        "_main-size": [null, "200px"],
      },
    ],
  },
  // ...and now with multiple items, which all shrink proportionally (by 50%)
  // to fit to the container, since they have the same (initial) flex-shrink val
  {
    items: [
      { "_main-size": ["80px", "40px"] },
      { "_main-size": ["40px", "20px"] },
      { "_main-size": ["30px", "15px"] },
      { "_main-size": ["250px", "125px"] },
    ],
  },
  // ...and now with positive flexibility specified. (should have no effect, so
  // everything still shrinks by the same proportion, since the flex-shrink
  // values are all the same).
  {
    items: [
      {
        flex: "4 3 100px",
        "_main-size": [null, "80px"],
      },
      {
        flex: "5 3 50px",
        "_main-size": [null, "40px"],
      },
      {
        flex: "0 3 100px",
        "_main-size": [null, "80px"],
      },
    ],
  },
  // ...and now with *different* flex-shrink values:
  {
    items: [
      {
        flex: "4 2 50px",
        "_main-size": [null, "30px"],
      },
      {
        flex: "5 3 50px",
        "_main-size": [null, "20px"],
      },
      {
        flex: "0 0 150px",
        "_main-size": [null, "150px"],
      },
    ],
  },
  // Same ratio as prev. testcase; making sure we handle float inaccuracy
  {
    items: [
      {
        flex: "4 20000000 50px",
        "_main-size": [null, "30px"],
      },
      {
        flex: "5 30000000 50px",
        "_main-size": [null, "20px"],
      },
      {
        flex: "0 0.0000001 150px",
        "_main-size": [null, "150px"],
      },
    ],
  },
  // Another "different flex-shrink values" testcase:
  {
    items: [
      {
        flex: "4 2 115px",
        "_main-size": [null, "69px"],
      },
      {
        flex: "5 1 150px",
        "_main-size": [null, "120px"],
      },
      {
        flex: "1 4 30px",
        "_main-size": [null, "6px"],
      },
      {
        flex: "1 0 5px",
        "_main-size": [null, "5px"],
      },
    ],
  },

  // ...and now with min-size (clamping the effects of flex-shrink on one item):
  {
    items: [
      {
        flex: "4 5 75px",
        "_min-main-size": "50px",
        "_main-size": [null, "50px"],
      },
      {
        flex: "5 5 100px",
        "_main-size": [null, "62.5px"],
      },
      {
        flex: "0 4 125px",
        "_main-size": [null, "87.5px"],
      },
    ],
  },

  // Test a min-size that's much larger than initial preferred size, but small
  // enough that our flexed size pushes us over it:
  {
    items: [
      {
        flex: "auto",
        "_min-main-size": "110px",
        "_main-size": ["50px", "125px"],
      },
      {
        flex: "auto",
        "_main-size": [null, "75px"],
      },
    ],
  },

  // Test a min-size that's much larger than initial preferred size, and is
  // even larger than our positively-flexed size, so that we have to increase it
  // (as a 'min violation') after we've flexed.
  {
    items: [
      {
        flex: "auto",
        "_min-main-size": "150px",
        "_main-size": ["50px", "150px"],
      },
      {
        flex: "auto",
        "_main-size": [null, "50px"],
      },
    ],
  },

  // Test min-size on multiple items simultaneously:
  {
    items: [
      {
        flex: "auto",
        "_min-main-size": "20px",
        "_main-size": [null, "20px"],
      },
      {
        flex: "9 auto",
        "_min-main-size": "150px",
        "_main-size": ["50px", "180px"],
      },
    ],
  },
  {
    items: [
      {
        flex: "1 1 0px",
        "_min-main-size": "90px",
        "_main-size": [null, "90px"],
      },
      {
        flex: "1 1 0px",
        "_min-main-size": "80px",
        "_main-size": [null, "80px"],
      },
      {
        flex: "1 1 40px",
        "_main-size": [null, "30px"],
      },
    ],
  },

  // Test a case where _min-main-size will be violated on different items in
  // successive iterations of the "resolve the flexible lengths" loop
  {
    items: [
      {
        flex: "1 2 100px",
        "_min-main-size": "90px",
        "_main-size": [null, "90px"],
      },
      {
        flex: "1 1 100px",
        "_min-main-size": "70px",
        "_main-size": [null, "70px"],
      },
      {
        flex: "1 1 100px",
        "_main-size": [null, "40px"],
      },
    ],
  },

  // Test some cases that have a min-size violation on one item and a
  // max-size violation on another:

  // Here, both items initially grow to 100px. That violates both
  // items' sizing constraints (it's smaller than the min-size and larger than
  // the max-size), so we clamp both of them and sum the clamping-differences:
  //
  //   (130px - 100px) + (50px - 100px) = (30px) + (-50px) = -20px
  //
  // This sum is negative, so (per spec) we freeze the item that had its
  // max-size violated (the second one) and restart the algorithm.  This time,
  // all the available space (200px - 50px = 150px) goes to the not-yet-frozen
  // first item, and that puts it above its min-size, so all is well.
  {
    items: [
      {
        flex: "auto",
        "_min-main-size": "130px",
        "_main-size": [null, "150px"],
      },
      {
        flex: "auto",
        "_max-main-size": "50px",
        "_main-size": [null, "50px"],
      },
    ],
  },

  // As above, both items initially grow to 100px, and that violates both items'
  // constraints. However, now the sum of the clamping differences is:
  //
  //   (130px - 100px) + (80px - 100px) = (30px) + (-20px) = 10px
  //
  // This sum is positive, so (per spec) we freeze the item that had its
  // min-size violated (the first one) and restart the algorithm. This time,
  // all the available space (200px - 130px = 70px) goes to the not-yet-frozen
  // second item, and that puts it below its max-size, so all is well.
  {
    items: [
      {
        flex: "auto",
        "_min-main-size": "130px",
        "_main-size": [null, "130px"],
      },
      {
        flex: "auto",
        "_max-main-size": "80px",
        "_main-size": [null, "70px"],
      },
    ],
  },

  // As above, both items initially grow to 100px, and that violates both items'
  // constraints. So we clamp both items and sum the clamping differences to
  // see what to do next.  The sum is:
  //
  //   (80px - 100px) + (120px - 100px) = (-20px) + (20px) = 0px
  //
  // Per spec, if the sum is 0, we're done -- we leave both items at their
  // clamped sizes.
  {
    items: [
      {
        flex: "auto",
        "_max-main-size": "80px",
        "_main-size": [null, "80px"],
      },
      {
        flex: "auto",
        "_min-main-size": "120px",
        "_main-size": [null, "120px"],
      },
    ],
  },

  // Test cases where flex-grow sums to less than 1:
  // ===============================================
  // This makes us treat the flexibilities like "fraction of free space"
  // instead of weights, so that e.g. a single item with "flex-grow: 0.1"
  // will only get 10% of the free space instead of all of the free space.

  // Basic cases where flex-grow sum is less than 1:
  {
    items: [
      {
        flex: "0.1 100px",
        "_main-size": [null, "110px"], // +10% of free space
      },
    ],
  },
  {
    items: [
      {
        flex: "0.8 0px",
        "_main-size": [null, "160px"], // +80% of free space
      },
    ],
  },

  // ... and now with two flex items:
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "110px"], // +40% of free space
      },
      {
        flex: "0.2 30px",
        "_main-size": [null, "50px"], // +20% of free space
      },
    ],
  },

  // ...and now with max-size modifying how much free space one item can take:
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "110px"], // +40% of free space
      },
      {
        flex: "0.2 30px",
        "_max-main-size": "35px",
        "_main-size": [null, "35px"], // +20% free space, then clamped
      },
    ],
  },
  // ...and now with a max-size smaller than our flex-basis:
  // (This makes us freeze the second item right away, before we compute
  // the initial free space.)
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "118px"], // +40% of 200px-70px-10px
      },
      {
        flex: "0.2 30px",
        "_max-main-size": "10px",
        "_main-size": [null, "10px"], // immediately frozen
      },
    ],
  },
  // ...and now with a max-size and a huge flex-basis, such that we initially
  // have negative free space, which makes the "% of [original] free space"
  // calculations a bit more subtle. We set the "original free space" after
  // we've clamped the second item (the first time the free space is positive).
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "118px"], // +40% of free space _after freezing
        // the other item_
      },
      {
        flex: "0.2 150px",
        "_max-main-size": "10px",
        "_main-size": [null, "10px"], // clamped immediately
      },
    ],
  },

  // Now with min-size modifying how much free space our items take:
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "110px"], // +40% of free space
      },
      {
        flex: "0.2 30px",
        "_min-main-size": "70px",
        "_main-size": [null, "70px"], // +20% free space, then clamped
      },
    ],
  },

  // ...and now with a large enough min-size that it prevents the other flex
  // item from taking its full desired portion of the original free space:
  {
    items: [
      {
        flex: "0.4 70px",
        "_main-size": [null, "80px"], // (Can't take my full +40% of
        // free space due to other item's
        // large min-size.)
      },
      {
        flex: "0.2 30px",
        "_min-main-size": "120px",
        "_main-size": [null, "120px"], // +20% free space, then clamped
      },
    ],
  },
  // ...and now with a large-enough min-size that it pushes the other flex item
  // to actually shrink a bit (with default "flex-shrink:1"):
  {
    items: [
      {
        flex: "0.3 30px",
        "_main-size": [null, "20px"], // -10px, instead of desired +45px
      },
      {
        flex: "0.2 20px",
        "_min-main-size": "180px",
        "_main-size": [null, "180px"], // +160px, instead of desired +30px
      },
    ],
  },

  // In this case, the items' flexibilities don't initially sum to < 1, but they
  // do after we freeze the third item for violating its max-size.
  {
    items: [
      {
        flex: "0.3 30px",
        "_main-size": [null, "75px"],
        // 1st loop: desires (0.3 / 5) * 150px = 9px. Tentatively granted.
        // 2nd loop: desires 0.3 * 150px = 45px. Tentatively granted.
        // 3rd loop: desires 0.3 * 150px = 45px. Granted +45px.
      },
      {
        flex: "0.2 20px",
        "_max-main-size": "30px",
        "_main-size": [null, "30px"],
        // First loop: desires (0.2 / 5) * 150px = 6px. Tentatively granted.
        // Second loop: desires 0.2 * 150px = 30px. Frozen at +10px.
      },
      {
        flex: "4.5 0px",
        "_max-main-size": "20px",
        "_main-size": [null, "20px"],
        // First loop: desires (4.5 / 5) * 150px = 135px. Frozen at +20px.
      },
    ],
  },

  // Make sure we calculate "original free space" correctly when one of our
  // flex items will be clamped right away, due to max-size preventing it from
  // growing at all:
  {
    // Here, the second flex item is effectively inflexible; it's
    // immediately frozen at 40px since we're growing & this item's max size
    // trivially prevents it from growing. This leaves us with an "original
    // free space" of 60px. The first flex item takes half of that, due to
    // its flex-grow value of 0.5.
    items: [
      {
        flex: "0.5 100px",
        "_main-size": [null, "130px"],
      },
      {
        flex: "1 98px",
        "_max-main-size": "40px",
        "_main-size": [null, "40px"],
      },
    ],
  },
  {
    // Same as previous example, but with a larger flex-basis on the second
    // element (which shouldn't ultimately matter, because its max size clamps
    // its size immediately anyway).
    items: [
      {
        flex: "0.5 100px",
        "_main-size": [null, "130px"],
      },
      {
        flex: "1 101px",
        "_max-main-size": "40px",
        "_main-size": [null, "40px"],
      },
    ],
  },

  {
    // Here, the third flex item is effectively inflexible; it's immediately
    // frozen at 0px since we're growing & this item's max size trivially
    // prevents it from growing. This leaves us with an "original free space" of
    // 100px. The first flex item takes 40px, and the third takes 50px, due to
    // their flex values of 0.4 and 0.5.
    items: [
      {
        flex: "0.4 50px",
        "_main-size": [null, "90px"],
      },
      {
        flex: "0.5 50px",
        "_main-size": [null, "100px"],
      },
      {
        flex: "0 90px",
        "_max-main-size": "0px",
        "_main-size": [null, "0px"],
      },
    ],
  },
  {
    // Same as previous example, but with slightly larger flex-grow values on
    // the first and second items, which sum to 1.0 and produce slightly larger
    // main sizes. This demonstrates that there's no discontinuity between the
    // "< 1.0 sum" to ">= 1.0 sum" behavior, in this situation at least.
    items: [
      {
        flex: "0.45 50px",
        "_main-size": [null, "95px"],
      },
      {
        flex: "0.55 50px",
        "_main-size": [null, "105px"],
      },
      {
        flex: "0 90px",
        "_max-main-size": "0px",
        "_main-size": [null, "0px"],
      },
    ],
  },

  // Test cases where flex-shrink sums to less than 1:
  // =================================================
  // This makes us treat the flexibilities more like "fraction of (negative)
  // free space" instead of weights, so that e.g. a single item with
  // "flex-shrink: 0.1" will only shrink by 10% of amount that it overflows
  // its container by.
  //
  // It gets a bit more complex when there are multiple flex items, because
  // flex-shrink is scaled by the flex-basis before it's used as a weight. But
  // even with that scaling, the general principal is that e.g. if the
  // flex-shrink values *sum* to 0.6, then the items will collectively only
  // shrink by 60% (and hence will still overflow).

  // Basic cases where flex-grow sum is less than 1:
  {
    items: [
      {
        flex: "0 0.1 300px",
        "_main-size": [null, "290px"], // +10% of (negative) free space
      },
    ],
  },
  {
    items: [
      {
        flex: "0 0.8 400px",
        "_main-size": [null, "240px"], // +80% of (negative) free space
      },
    ],
  },

  // ...now with two flex items, with the same flex-basis value:
  {
    items: [
      {
        flex: "0 0.4 150px",
        "_main-size": [null, "110px"], // +40% of (negative) free space
      },
      {
        flex: "0 0.2 150px",
        "_main-size": [null, "130px"], // +20% of (negative) free space
      },
    ],
  },

  // ...now with two flex items, with different flex-basis values (and hence
  // differently-scaled flex factors):
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "76px"],
      },
      {
        flex: "0 0.1 200px",
        "_main-size": [null, "184px"],
      },
    ],
    // Notes:
    //  - Free space: -100px
    //  - Sum of flex-shrink factors: 0.3 + 0.1 = 0.4
    //  - Since that sum ^ is < 1, we'll only distribute that fraction of
    //    the free space. We'll distribute: -100px * 0.4 = -40px
    //
    //  - 1st item's scaled flex factor:  0.3 * 100px = 30
    //  - 2nd item's scaled flex factor:  0.1 * 200px = 20
    //  - 1st item's share of distributed free space: 30/(30+20) = 60%
    //  - 2nd item's share of distributed free space: 20/(30+20) = 40%
    //
    // SO:
    //  - 1st item gets 60% * -40px = -24px.  100px-24px = 76px
    //  - 2nd item gets 40% * -40px = -16px.  200px-16px = 184px
  },

  // ...now with min-size modifying how much one item can shrink:
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "70px"],
      },
      {
        flex: "0 0.1 200px",
        "_min-main-size": "190px",
        "_main-size": [null, "190px"],
      },
    ],
    // Notes:
    //  - We proceed as in previous testcase, but clamp the second flex item
    //    at its min main size.
    //  - After that point, we have a total flex-shrink of = 0.3, so we
    //    distribute 0.3 * -100px = -30px to the remaining unfrozen flex
    //    items. Since there's only one unfrozen item left, it gets all of it.
  },

  // ...now with min-size larger than our flex-basis:
  // (This makes us freeze the second item right away, before we compute
  // the initial free space.)
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "55px"], // +30% of 200px-100px-250px
      },
      {
        flex: "0 0.1 200px",
        "_min-main-size": "250px",
        "_main-size": [null, "250px"], // immediately frozen
      },
    ],
    // (Same as previous example, except the min-main-size prevents the
    // second item from shrinking at all)
  },

  // ...and now with a min-size and a small flex-basis, such that we initially
  // have positive free space, which makes the "% of [original] free space"
  // calculations a bit more subtle. We set the "original free space" after
  // we've clamped the second item (the first time the free space is negative).
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "70px"],
      },
      {
        flex: "0 0.1 50px",
        "_min-main-size": "200px",
        "_main-size": [null, "200px"],
      },
    ],
  },

  // Now with max-size making an item shrink more than its flex-shrink value
  // calls for:
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "70px"],
      },
      {
        flex: "0 0.1 200px",
        "_max-main-size": "150px",
        "_main-size": [null, "150px"],
      },
    ],
    // Notes:
    //  - We proceed as in an earlier testcase, but clamp the second flex item
    //    at its max main size.
    //  - After that point, we have a total flex-shrink of = 0.3, so we
    //    distribute 0.3 * -100px = -30px to the remaining unfrozen flex
    //    items. Since there's only one unfrozen item left, it gets all of it.
  },

  // ...and now with a small enough max-size that it prevents the other flex
  // item from taking its full desired portion of the (negative) original free
  // space:
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "90px"],
      },
      {
        flex: "0 0.1 200px",
        "_max-main-size": "110px",
        "_main-size": [null, "110px"],
      },
    ],
    // Notes:
    //  - We proceed as in an earlier testcase, but clamp the second flex item
    //    at its max main size.
    //  - After that point, we have a total flex-shrink of 0.3, which would
    //    have us distribute 0.3 * -100px = -30px to the (one) remaining
    //    unfrozen flex item. But our remaining free space is only -10px at
    //    that point, so we distribute that instead.
  },

  // ...and now with a small enough max-size that it pushes the other flex item
  // to actually grow a bit (with custom "flex-grow: 1" for this testcase):
  {
    items: [
      {
        flex: "1 0.3 100px",
        "_main-size": [null, "120px"],
      },
      {
        flex: "1 0.1 200px",
        "_max-main-size": "80px",
        "_main-size": [null, "80px"],
      },
    ],
  },

  // In this case, the items' flexibilities don't initially sum to < 1, but they
  // do after we freeze the third item for violating its min-size.
  {
    items: [
      {
        flex: "0 0.3 100px",
        "_main-size": [null, "76px"],
      },
      {
        flex: "0 0.1 150px",
        "_main-size": [null, "138px"],
      },
      {
        flex: "0 0.8 10px",
        "_min-main-size": "40px",
        "_main-size": [null, "40px"],
      },
    ],
    // Notes:
    //  - We immediately freeze the 3rd item, since we're shrinking and its
    //    min size obviously prevents it from shrinking at all.  This leaves
    //    200px - 100px - 150px - 40px = -90px of "initial free space".
    //
    //  - Our remaining flexible items have a total flex-shrink of 0.4,
    //    so we can distribute a total of 0.4 * -90px = -36px
    //
    //  - We distribute that space using *scaled* flex factors:
    //    * 1st item's scaled flex factor:  0.3 * 100px = 30
    //    * 2nd item's scaled flex factor:  0.1 * 150px = 15
    //   ...which means...
    //    * 1st item's share of distributed free space: 30/(30+15) = 2/3
    //    * 2nd item's share of distributed free space: 15/(30+15) = 1/3
    //
    // SO:
    //  - 1st item gets 2/3 * -36px = -24px. 100px - 24px = 76px
    //  - 2nd item gets 1/3 * -36px = -12px. 150px - 12px = 138px
  },

  // In this case, the items' flexibilities sum to > 1, in part due to an item
  // that *can't actually shrink* due to its 0 flex-basis (which gives it a
  // "scaled flex factor" of 0). This prevents us from triggering the special
  // behavior for flexibilities that sum to less than 1, and as a result, the
  // first item ends up absorbing all of the free space.
  {
    items: [
      {
        flex: "0 .5 300px",
        "_main-size": [null, "200px"],
      },
      {
        flex: "0 5 0px",
        "_main-size": [null, "0px"],
      },
    ],
  },

  // This case is similar to the one above, but with a *barely* nonzero base
  // size for the second item. This should produce a result similar to the case
  // above. (In particular, we should first distribute a very small amount of
  // negative free space to the second item, getting it to approximately zero,
  // and distribute the bulk of the negative free space to the first item,
  // getting it to approximately 200px.)
  {
    items: [
      {
        flex: "0 .5 300px",
        "_main-size": [null, "200px"],
      },
      {
        flex: "0 1 0.01px",
        "_main-size": [null, "0px"],
      },
    ],
  },
  // This case is similar to the ones above, but now we've increased the
  // flex-shrink value on the second-item so that it claims enough of the
  // negative free space to go below its min-size (0px). So, it triggers a min
  // violation & is frozen. For the loop *after* the min violation, the sum of
  // the remaining flex items' flex-shrink values is less than 1, so we trigger
  // the special <1 behavior and only distribute half of the remaining
  // (negative) free space to the first item (instead of all of it).
  {
    items: [
      {
        flex: "0 .5 300px",
        "_main-size": [null, "250px"],
      },
      {
        flex: "0 5 0.01px",
        "_main-size": [null, "0px"],
      },
    ],
  },
];