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test(compat/flatMapDeep): add cases for deep flattening with and without iteratee - #1859
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# Conflicts: # src/compat/array/flatMapDeep.spec.ts
raon0211
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Aug 8, 2026
gwennlbh
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Sep 8, 2026
##### [v1.52.0](https://github.com/toss/es-toolkit/blob/HEAD/CHANGELOG.md#Version-v1520) Released on August 28th, 2026. - Added the `es-toolkit/iterator` entrypoint, a lazy iterator module with `chunk`, `count`, `dropWhile`, `head`, `iterate`, `partition`, `range`, `scan`, `takeWhile`, `uniqBy`, and `zip` (\[[#1815](toss/es-toolkit#1815)]), plus `cartesianProduct` (\[[#2031](toss/es-toolkit#2031)]). The same functions are also available from `es-toolkit/fp/iterator`. - Added `defer` and `deferAsync` to `es-toolkit/util`. (\[[#2032](toss/es-toolkit#2032)]) - Added `flowAsync` to `es-toolkit/fp`, a promise-aware left-to-right composition. (\[[#2033](toss/es-toolkit#2033)]) - Added the `EmptyObject`, `IsEqual`, `JSONValue`, `Primitive`, `SetOptional`, `SetRequired`, and `UnknownRecord` types. (\[[#2044](toss/es-toolkit#2044)]) - Fixed `merge` to infer the deep merged return type, and exported the `Merge` type. (\[[#1959](toss/es-toolkit#1959)]) - Fixed `omitBy` and `pickBy` to type numeric callback keys as strings, and exported the `ObjectKeys` type. (\[[#2037](toss/es-toolkit#2037)]) - Fixed `attempt` and `attemptAsync` to default their error type parameter to `unknown`. (\[[#2052](toss/es-toolkit#2052)]) The following bring `es-toolkit/compat` closer to Lodash. Behavior for the affected edge cases now matches Lodash, so results may differ if you relied on the previous output. - Fixed `compat/debounce` to skip the `maxWait` invocation when both `leading` and `trailing` are `false`. (\[[#1678](toss/es-toolkit#1678)]) - Fixed `compat/toString` to convert objects with a custom `valueOf`. (\[[#2034](toss/es-toolkit#2034)]) - Fixed `compat/mergeWith` to assign `null` values in array sources. (\[[#1929](toss/es-toolkit#1929)]) - Fixed `compat/has` and `compat/hasIn` to normalize the `-0` path key. (\[[#2035](toss/es-toolkit#2035)]) - Fixed `compat/differenceWith` and `compat/without` to normalize `-0` to `0`. (\[[#2049](toss/es-toolkit#2049)]) - Fixed `compat/findLastIndex` to convert `fromIndex` to an integer. (\[[#2047](toss/es-toolkit#2047)]) - Fixed `compat/xorWith` to match Lodash when no comparator is given. (\[[#2057](toss/es-toolkit#2057)]) - Covered the new iterator entrypoints in the dist and browser compatibility checks. (\[[#2030](toss/es-toolkit#2030)]) - Made the agent skills portable when installed on their own. (\[[#2054](toss/es-toolkit#2054)]) - Fixed documentation typos and the Deno install commands. (\[[#2062](toss/es-toolkit#2062)]) ##### [v1.51.0](https://github.com/toss/es-toolkit/blob/HEAD/CHANGELOG.md#Version-v1510) Released on August 17th, 2026. - Added the `es-toolkit/bigint` entrypoint: `bigint` counterparts of the math functions (`sum`, `sumBy`, `max`, `min`, `maxBy`, `minBy`, `clamp`, `inRange`, `median`, `medianBy`, `percentile`, `range`, `rangeRight`), kept separate so the `number` implementations stay unchanged. (\[[#1966](toss/es-toolkit#1966)]) - Added `dedent`, which removes common leading whitespace from template strings. (\[[#1679](toss/es-toolkit#1679)]) - Added `deepFreeze` for recursively freezing objects. (\[[#1680](toss/es-toolkit#1680)]) - Added `mapValuesAsync` and `mapKeysAsync`. (\[[#1544](toss/es-toolkit#1544)]) - Added `toPascalCaseKeys`, `toKebabCaseKeys`, and `toConstantCaseKeys`, completing the object key casing family. (\[[#1984](toss/es-toolkit#1984)]) - Exported the `ToCamelCaseKeys`, `ToPascalCaseKeys`, `ToSnakeCaseKeys`, `ToKebabCaseKeys`, and `ToConstantCaseKeys` types. (\[[#1651](toss/es-toolkit#1651)]) - Added a `preserveArrays` option to `flattenObject`. (\[[#974](toss/es-toolkit#974)]) - Fixed `retry` to pass the last error to the `delay` callback (\[[#1759](toss/es-toolkit#1759)]) and to throw the last attempt's error without applying a final delay (\[[#1901](toss/es-toolkit#1901)]). - Fixed `mergeWith` and `toMerged` to handle mixed array/object types consistently with `merge`. (\[[#2026](toss/es-toolkit#2026)]) - Fixed `pullAt` to remove the correct elements with negative indices. (\[[#1613](toss/es-toolkit#1613)]) - Fixed `at`, `pullAt`, `orderBy`, and `sortBy` to accept readonly arrays. (\[[#2016](toss/es-toolkit#2016)]) - Moved `limitAsync` from the array to the promise category. (\[[#2022](toss/es-toolkit#2022)]) - Included the NOTICE file in the published npm and JSR packages. (\[[#2020](toss/es-toolkit#2020)]) The following bring `es-toolkit/compat` closer to Lodash. Behavior for the affected edge cases now matches Lodash, so results may differ if you relied on the previous output. - Added `entries` and `entriesIn`. (\[[#1874](toss/es-toolkit#1874)]) - Fixed `compat/isMatch` and `compat/isMatchWith` to handle object source patterns against primitive and non-plain-object targets like Lodash. (\[[#1432](toss/es-toolkit#1432)]) - Fixed `compat/set` to block `constructor.prototype` paths, preventing prototype pollution. (\[[#1904](toss/es-toolkit#1904)]) - Fixed `compat/find` to respect array-like `length` (\[[#1958](toss/es-toolkit#1958)]) and to convert `fromIndex` to an integer (\[[#1961](toss/es-toolkit#1961)]), and `compat/indexOf` to convert `fromIndex` to an integer when searching for `NaN` (\[[#1951](toss/es-toolkit#1951)]). - Fixed `compat/orderBy` to resolve unresolved deep paths and nullish elements to `undefined` (\[[#2010](toss/es-toolkit#2010)]), to exclude the `length` property from array-like values (\[[#2002](toss/es-toolkit#2002)]), and to read the criterion property from primitive values (\[[#1903](toss/es-toolkit#1903)]). - Fixed `compat/toPath` to split unquoted dotted keys inside brackets. (\[[#1899](toss/es-toolkit#1899)]) - Fixed `compat/omit` to treat a key array as a single deep path. (\[[#1902](toss/es-toolkit#1902)]) - Fixed `compat/map` to make the iteratee optional with an identity default. (\[[#1928](toss/es-toolkit#1928)]) - Fixed `compat/size` to count combined Unicode symbols as single characters. (\[[#1900](toss/es-toolkit#1900)]) - Fixed `compat/intersectionBy` to support number, object, and nullish iteratee shorthands (\[[#1993](toss/es-toolkit#1993)]), and `compat/intersectionWith` to apply the comparator when deduplicating the first array (\[[#1953](toss/es-toolkit#1953)]). - Fixed `compat/difference`, `compat/differenceBy`, `compat/uniqBy`, and `compat/unionBy` to normalize `-0` to `0`. (\[[#2007](toss/es-toolkit#2007)]) - Fixed `compat/maxBy` and `compat/minBy` to skip nullish iteratee values (\[[#1927](toss/es-toolkit#1927)]), and `compat/meanBy` to skip `undefined` values when averaging (\[[#1978](toss/es-toolkit#1978)]). - Fixed `compat/some`, `compat/template` (\[[#2009](toss/es-toolkit#2009)]), and `compat/fill` (\[[#1952](toss/es-toolkit#1952)]) to gate guard handling with `isIterateeCall`. - Fixed `compat/iteratee` to treat a boolean as a property shorthand. (\[[#1941](toss/es-toolkit#1941)]) - Fixed `compat/reverse` to support array-like objects and `arguments`. (\[[#2008](toss/es-toolkit#2008)]) - Fixed `compat/toArray` to convert non-array-like iterables. (\[[#1999](toss/es-toolkit#1999)]) - Fixed `compat/toString` to render nested nullish values like Lodash. (\[[#1992](toss/es-toolkit#1992)]) - Fixed `compat/zipObject` to treat `null` keys and values as empty arrays. (\[[#2005](toss/es-toolkit#2005)]) - Fixed `compat/sampleSize` to clamp the default size to the collection length. (\[[#2003](toss/es-toolkit#2003)]) - Fixed `compat/takeWhile`, `compat/takeRightWhile`, and `compat/uniqBy` to support string inputs. (\[[#2004](toss/es-toolkit#2004)]) - Fixed `compat/chunk` to return an empty array for an empty collection with an `Infinity` size. (\[[#1995](toss/es-toolkit#1995)]) - Fixed `compat/lastIndexOf` to read holes in sparse arrays as `undefined`. (\[[#1977](toss/es-toolkit#1977)]) - Fixed `compat/last` to return `undefined` for empty array-like inputs. (\[[#1954](toss/es-toolkit#1954)]) - Fixed `compat/pullAll` to return the array as-is when `values` is nullish. (\[[#1962](toss/es-toolkit#1962)]) - Added a browser compatibility test suite. (\[[#2012](toss/es-toolkit#2012)]) - Improved documentation, JSDoc accuracy, tests, and internal refactoring across `compat` and the docs site. (\[[#1622](toss/es-toolkit#1622)], \[[#1789](toss/es-toolkit#1789)], \[[#1824](toss/es-toolkit#1824)], \[[#1844](toss/es-toolkit#1844)], \[[#1849](toss/es-toolkit#1849)], \[[#1854](toss/es-toolkit#1854)], \[[#1855](toss/es-toolkit#1855)], \[[#1859](toss/es-toolkit#1859)], \[[#1860](toss/es-toolkit#1860)], \[[#1868](toss/es-toolkit#1868)], \[[#1871](toss/es-toolkit#1871)], \[[#1887](toss/es-toolkit#1887)], \[[#1898](toss/es-toolkit#1898)], \[[#1933](toss/es-toolkit#1933)], \[[#1939](toss/es-toolkit#1939)], \[[#1947](toss/es-toolkit#1947)], \[[#1950](toss/es-toolkit#1950)], \[[#1955](toss/es-toolkit#1955)], \[[#1956](toss/es-toolkit#1956)], \[[#1957](toss/es-toolkit#1957)], \[[#1960](toss/es-toolkit#1960)], \[[#1963](toss/es-toolkit#1963)], \[[#1964](toss/es-toolkit#1964)], \[[#1968](toss/es-toolkit#1968)], \[[#1969](toss/es-toolkit#1969)], \[[#1970](toss/es-toolkit#1970)], \[[#1972](toss/es-toolkit#1972)], \[[#1979](toss/es-toolkit#1979)], \[[#1985](toss/es-toolkit#1985)], \[[#2000](toss/es-toolkit#2000)], \[[#2001](toss/es-toolkit#2001)], \[[#2021](toss/es-toolkit#2021)], \[[#2025](toss/es-toolkit#2025)], \[[#2027](toss/es-toolkit#2027)]) We sincerely thank [@Antoliny0919](https://github.com/Antoliny0919), [@D-Sketon](https://github.com/D-Sketon), [@kojesung](https://github.com/kojesung), [@chuenchen309](https://github.com/chuenchen309), [@mariazuheros](https://github.com/mariazuheros), [@DongEun02](https://github.com/DongEun02), [@raon0211](https://github.com/raon0211), [@sukvvon](https://github.com/sukvvon), [@racgoo](https://github.com/racgoo), [@dayongkr](https://github.com/dayongkr), [@Kropiunig](https://github.com/Kropiunig), [@ssi02014](https://github.com/ssi02014), [@sarathfrancis90](https://github.com/sarathfrancis90), [@mym0404](https://github.com/mym0404), [@mlnwns](https://github.com/mlnwns), [@kdelay](https://github.com/kdelay), [@gwagjiug](https://github.com/gwagjiug), [@dohwi](https://github.com/dohwi), [@blro0319](https://github.com/blro0319), [@benedictleejh](https://github.com/benedictleejh), [@amir-rezaei](https://github.com/amir-rezaei), [@ianzone](https://github.com/ianzone), [@sen2y](https://github.com/sen2y), [@rossyman](https://github.com/rossyman), [@eunwoo-levi](https://github.com/eunwoo-levi), [@ramong26](https://github.com/ramong26), [@Gdm0714](https://github.com/Gdm0714), and everyone else who contributed. We appreciate your great efforts! Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
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Summay
https://github.com/lodash/lodash/blob/6a2cc1dfcf7634fea70d1bc5bd22db453df67b42/test/flatMap-methods.spec.js
I think
flatMapDeepshould be tested with deeply nested arrays to properly verify its behavior. Since these tests were copied directly from Lodash, though, that scenario isn't actually being covered.This is probably something that should be tested in Lodash as well. It seems to be one of the downsides of grouping tests by shared behavior rather than by individual functionality 😡