Integration Testing#

To ensure Arrow implementations are interoperable between each other, the Arrow project includes cross-language integration tests which are regularly run as Continuous Integration tasks.

The integration tests exercise compliance with several Arrow specifications: the IPC format, the Flight RPC protocol, and the C Data Interface.


Our strategy for integration testing between Arrow implementations is:

  • Test datasets are specified in a custom human-readable, JSON-based format designed exclusively for Arrow’s integration tests.

  • The JSON files are generated by the integration test harness. Different files are used to represent different data types and features, such as numerics, lists, dictionary encoding, etc. This makes it easier to pinpoint incompatibilities than if all data types were represented in a single file.

  • Each implementation provides entry points capable of converting between the JSON and the Arrow in-memory representation, and of exposing Arrow in-memory data using the desired format.

  • Each format (whether Arrow IPC, Flight or the C Data Interface) is tested for all supported pairs of (producer, consumer) implementations. The producer typically reads a JSON file, converts it to in-memory Arrow data, and exposes this data using the format under test. The consumer reads the data in the said format and converts it back to Arrow in-memory data; it also reads the same JSON file as the producer, and validates that both datasets are identical.

Example: IPC format#

Let’s say we are testing Arrow C++ as a producer and Arrow Java as a consumer of the Arrow IPC format. Testing a JSON file would go as follows:

  1. A C++ executable reads the JSON file, converts it into Arrow in-memory data and writes an Arrow IPC file (the file paths are typically given on the command line).

  2. A Java executable reads the JSON file, converts it into Arrow in-memory data; it also reads the Arrow IPC file generated by C++. Finally, it validates that both Arrow in-memory datasets are equal.

Example: C Data Interface#

Now, let’s say we are testing Arrow Go as a producer and Arrow C# as a consumer of the Arrow C Data Interface.

  1. The integration testing harness allocates a C ArrowArray structure on the heap.

  2. A Go in-process entrypoint (for example a C-compatible function call) reads a JSON file and exports one of its record batches into the ArrowArray structure.

  3. A C# in-process entrypoint reads the same JSON file, converts the same record batch into Arrow in-memory data; it also imports the record batch exported by Arrow Go in the ArrowArray structure. It validates that both record batches are equal, and then releases the imported record batch.

  4. Depending on the implementation languages’ abilities, the integration testing harness may assert that memory consumption remained identical (i.e., that the exported record batch didn’t leak).

  5. At the end, the integration testing harness deallocates the ArrowArray structure.

Running integration tests#

The integration test data generator and runner are implemented inside the Archery utility. You need to install the integration component of archery:

$ pip install -e "dev/archery[integration]"

The integration tests are run using the archery integration command.

$ archery integration --help

In order to run integration tests, you’ll first need to build each component you want to include. See the respective developer docs for C++, Java, etc. for instructions on building those.

Some languages may require additional build options to enable integration testing. For C++, for example, you need to add -DARROW_BUILD_INTEGRATION=ON to your cmake command.

Depending on which components you have built, you can enable and add them to the archery test run. For example, if you only have the C++ project built and want to run the Arrow IPC integration tests, run:

archery integration --run-ipc --with-cpp=1

For Java, it may look like:

export ARROW_JAVA_INTEGRATION_JAR=$JAVA_DIR/tools/target/arrow-tools-$VERSION-jar-with-dependencies.jar
archery integration --run-ipc --with-cpp=1 --with-java=1

To run all tests, including Flight and C Data Interface integration tests, do:

archery integration --with-all --run-flight --run-ipc --run-c-data

Note that we run these tests in continuous integration, and the CI job uses docker-compose. You may also run the docker-compose job locally, or at least refer to it if you have questions about how to build other languages or enable certain tests.

See Running Docker Builds for more information about the project’s docker-compose configuration.

JSON test data format#

A JSON representation of Arrow columnar data is provided for cross-language integration testing purposes. This representation is not canonical but it provides a human-readable way of verifying language implementations.

See here for some examples of this JSON data.

The high level structure of a JSON integration test files is as follows:

Data file

  "schema": /*Schema*/,
  "batches": [ /*RecordBatch*/ ],
  "dictionaries": [ /*DictionaryBatch*/ ],

All files contain schema and batches, while dictionaries is only present if there are dictionary type fields in the schema.


  "fields" : [
    /* Field */
  "metadata" : /* Metadata */


  "name" : "name_of_the_field",
  "nullable" : /* boolean */,
  "type" : /* Type */,
  "children" : [ /* Field */ ],
  "dictionary": {
    "id": /* integer */,
    "indexType": /* Type */,
    "isOrdered": /* boolean */
  "metadata" : /* Metadata */

The dictionary attribute is present if and only if the Field corresponds to a dictionary type, and its id maps onto a column in the DictionaryBatch. In this case the type attribute describes the value type of the dictionary.

For primitive types, children is an empty array.


null |
[ {
  "key": /* string */,
  "value": /* string */
} ]

A key-value mapping of custom metadata. It may be omitted or null, in which case it is considered equivalent to [] (no metadata). Duplicated keys are not forbidden here.


  "name" : "null|struct|list|largelist|listview|largelistview|fixedsizelist|union|int|floatingpoint|utf8|largeutf8|binary|largebinary|utf8view|binaryview|fixedsizebinary|bool|decimal|date|time|timestamp|interval|duration|map|runendencoded"

A Type will have other fields as defined in Schema.fbs depending on its name.


  "name" : "int",
  "bitWidth" : /* integer */,
  "isSigned" : /* boolean */


  "name" : "floatingpoint",
  "precision" : "HALF|SINGLE|DOUBLE"


  "name" : "fixedsizebinary",
  "byteWidth" : /* byte width */


  "name" : "decimal",
  "precision" : /* integer */,
  "scale" : /* integer */


  "name" : "timestamp",
  "unit" : "$TIME_UNIT",
  "timezone": "$timezone"


“timezone” is an optional string.


  "name" : "duration",
  "unit" : "$TIME_UNIT"


  "name" : "date",
  "unit" : "DAY|MILLISECOND"


  "name" : "time",
  "unit" : "$TIME_UNIT",
  "bitWidth": /* integer: 32 or 64 */


  "name" : "interval",
  "unit" : "YEAR_MONTH|DAY_TIME"


  "name" : "union",
  "mode" : "SPARSE|DENSE",
  "typeIds" : [ /* integer */ ]

The typeIds field in Union are the codes used to denote which member of the union is active in each array slot. Note that in general these discriminants are not identical to the index of the corresponding child array.


  "name": "list"

The type that the list is a “list of” will be included in the Field’s “children” member, as a single Field there. For example, for a list of int32,

  "name": "list_nullable",
  "type": {
    "name": "list"
  "nullable": true,
  "children": [
      "name": "item",
      "type": {
        "name": "int",
        "isSigned": true,
        "bitWidth": 32
      "nullable": true,
      "children": []


  "name": "fixedsizelist",
  "listSize": /* integer */

This type likewise comes with a length-1 “children” array.


  "name": "struct"

The Field’s “children” contains an array of Fields with meaningful names and types.


  "name": "map",
  "keysSorted": /* boolean */

The Field’s “children” contains a single struct field, which itself contains 2 children, named “key” and “value”.


  "name": "null"


  "name": "runendencoded"

The Field’s “children” should be exactly two child fields. The first child must be named “run_ends”, be non-nullable and be either an int16, int32, or int64 type field. The second child must be named “values”, but can be of any type.

Extension types are, as in the IPC format, represented as their underlying storage type plus some dedicated field metadata to reconstruct the extension type. For example, assuming a “uuid” extension type backed by a FixedSizeBinary(16) storage, here is how a “uuid” field would be represented:

  "name" : "name_of_the_field",
  "nullable" : /* boolean */,
  "type" : {
     "name" : "fixedsizebinary",
     "byteWidth" : 16
  "children" : [],
  "metadata" : [
     {"key": "ARROW:extension:name", "value": "uuid"},
     {"key": "ARROW:extension:metadata", "value": "uuid-serialized"}


  "count": /* integer number of rows */,
  "columns": [ /* FieldData */ ]


  "id": /* integer */,
  "data": [ /* RecordBatch */ ]


  "name": "field_name",
  "count" "field_length",
  "$BUFFER_TYPE": /* BufferData */
  "$BUFFER_TYPE": /* BufferData */
  "children": [ /* FieldData */ ]

The “name” member of a Field in the Schema corresponds to the “name” of a FieldData contained in the “columns” of a RecordBatch. For nested types (list, struct, etc.), Field’s “children” each have a “name” that corresponds to the “name” of a FieldData inside the “children” of that FieldData. For FieldData inside of a DictionaryBatch, the “name” field does not correspond to anything.

Here $BUFFER_TYPE is one of VALIDITY, OFFSET (for variable-length types, such as strings and lists), TYPE_ID (for unions), or DATA.

BufferData is encoded based on the type of buffer:

  • VALIDITY: a JSON array of 1 (valid) and 0 (null). Data for non-nullable Field still has a VALIDITY array, even though all values are 1.

  • OFFSET: a JSON array of integers for 32-bit offsets or string-formatted integers for 64-bit offsets.

  • TYPE_ID: a JSON array of integers.

  • DATA: a JSON array of encoded values.

  • VARIADIC_DATA_BUFFERS: a JSON array of data buffers represented as hex encoded strings.

  • VIEWS: a JSON array of encoded views, which are JSON objects with:

    • SIZE: an integer indicating the size of the view,

    • INLINED: an encoded value (this field will be present if SIZE is smaller than 12, otherwise the next three fields will be present),

    • PREFIX_HEX: the first four bytes of the view encoded as hex,

    • BUFFER_INDEX: the index in VARIADIC_DATA_BUFFERS of the buffer viewed,

    • OFFSET: the offset in the buffer viewed.

The value encoding for DATA is different depending on the logical type:

  • For boolean type: an array of 1 (true) and 0 (false).

  • For integer-based types (including timestamps): an array of JSON numbers.

  • For 64-bit integers: an array of integers formatted as JSON strings, so as to avoid loss of precision.

  • For floating point types: an array of JSON numbers. Values are limited to 3 decimal places to avoid loss of precision.

  • For binary types, an array of uppercase hex-encoded strings, so as to represent arbitrary binary data.

  • For UTF-8 string types, an array of JSON strings.

For “list” and “largelist” types, BufferData has VALIDITY and OFFSET, and the rest of the data is inside “children”. These child FieldData contain all of the same attributes as non-child data, so in the example of a list of int32, the child data has VALIDITY and DATA.

For “fixedsizelist”, there is no OFFSET member because the offsets are implied by the field’s “listSize”.

Note that the “count” for these child data may not match the parent “count”. For example, if a RecordBatch has 7 rows and contains a FixedSizeList of listSize 4, then the data inside the “children” of that FieldData will have count 28.

For “null” type, BufferData does not contain any buffers.

Archery Integration Test Cases#

This list can make it easier to understand what manual testing may need to be done for any future Arrow Format changes by knowing what cases the automated integration testing actually tests.

There are two types of integration test cases: the ones populated on the fly by the data generator in the Archery utility, and gold files that exist in the arrow-testing repository.

Data Generator Tests#

This is the high-level description of the cases which are generated and tested using the archery integration command (see get_generated_json_files in

  • Primitive Types - No Batches - Various Primitive Values - Batches with Zero Length - String and Binary Large offset cases

  • Null Type * Trivial Null batches

  • Decimal128

  • Decimal256

  • DateTime with various units

  • Durations with various units

  • Intervals - MonthDayNano interval is a separate case

  • Map Types - Non-Canonical Maps

  • Nested Types - Lists - Structs - Lists with Large Offsets

  • Unions

  • Custom Metadata

  • Schemas with Duplicate Field Names

  • Dictionary Types - Signed indices - Unsigned indices - Nested dictionaries

  • Run end encoded

  • Binary view and string view

  • List view and large list view

  • Extension Types

Gold File Integration Tests#

Pre-generated json and arrow IPC files (both file and stream format) exist in the arrow-testing repository in the data/arrow-ipc-stream/integration directory. These serve as gold files that are assumed to be correct for use in testing. They are referenced by in the code for the Archery utility. Below are the test cases which are covered by them:

  • Backwards Compatibility

    • The following cases are tested using the 0.14.1 format:

      • datetime

      • decimals

      • dictionaries

      • intervals

      • maps

      • nested types (list, struct)

      • primitives

      • primitive with no batches

      • primitive with zero length batches

    • The following is tested for 0.17.1 format:

      • unions

  • Endianness

    • The following cases are tested with both Little Endian and Big Endian versions for auto conversion

      • custom metadata

      • datetime

      • decimals

      • decimal256

      • dictionaries

      • dictionaries with unsigned indices

      • record batches with duplicate fieldnames

      • extension types

      • interval types

      • map types

      • non-canonical map data

      • nested types (lists, structs)

      • nested dictionaries

      • nested large offset types

      • nulls

      • primitive data

      • large offset binary and strings

      • primitives with no batches included

      • primitive batches with zero length

      • recursive nested types

      • union types

  • Compression tests

    • LZ4

    • ZSTD

  • Batches with Shared Dictionaries