futhark test [options…] infiles…


This tool is used to test Futhark programs based on input/output datasets. If a directory is given, all contained files with a .fut extension are considered.

A Futhark test program is an ordinary Futhark program, with at least one test block describing input/output test cases and possibly other options. A test block consists of commented-out text with the following overall format:


The description is an arbitrary (and possibly multiline) human-readable explanation of the test program. It is separated from the test cases by a line containing just ==. Any comment starting at the beginning of the line, and containing a line consisting of just ==, will be considered a test block. The format of a test case is as follows:

[tags { tags... }]
[entry: names...]
[compiled|nobench|random] input ({ values... } | @ filename)
output { values... } | auto output | error: regex

If compiled is present before the input keyword, this test case will never be passed to the interpreter. This is useful for test cases that are annoyingly slow to interpret. The nobench keyword is for data sets that are too small to be worth benchmarking, and only has meaning to futhark-bench.

If input is preceded by random, the text between the curly braces must consist of a sequence of Futhark types, including sizes in the case of arrays. When futhark test is run, a file located in a data/ subdirectory, containing values of the indicated types and shapes is, automatically constructed with futhark-dataset. Apart from sizes, integer constants (with or without type suffix) are also permitted.

If input is followed by an @ and a file name (which must not contain any whitespace) instead of curly braces, values will be read from the indicated file. This is recommended for large data sets. This notation cannot be used with random input.

After the input block, the expected result of the test case is written as either output followed by another block of values, or an expected run-time error, in which a regular expression can be used to specify the exact error message expected. If no regular expression is given, any error message is accepted. If neither output nor error is given, the program will be expected to execute succesfully, but its output will not be validated.

If output is preceded by auto (as in auto output), the expected values are automatically generated by compiling the program with futhark-c and recording its result for the given input (which must not fail). This is usually only useful for testing or benchmarking alternative compilers, and not for testing the correctness of Futhark programs.

Alternatively, instead of input-output pairs, the test cases can simply be a description of an expected compile time type error:

error: regex

This is used to test the type checker.

By default, both the interpreter and compiler is run on all test cases (except those that have specified compiled), although this can be changed with command-line options to futhark test.

Tuple syntax is not supported when specifying input and output values. Instead, you can write an N-tuple as its constituent N values. Beware of syntax errors in the values - the errors reported by futhark test are very poor.

An optional tags specification is permitted in the first test block. This section can contain arbitrary tags that classify the benchmark:

tags { names... }

Tag are sequences of alphanumeric characters, dashes, and underscores, with each tag seperated by whitespace. Any program with the disable tag is ignored by futhark test.

Another optional directive is entry, which specifies the entry point to be used for testing. This is useful for writing programs that test libraries with multiple entry points. Multiple entry points can be specified on the same line by separating them with space, and they will all be tested with the same input/output pairs. The entry directive affects subsequent input-output pairs in the same comment block, and may only be present immediately preceding these input-output pairs. If no entry is given, main is assumed. See below for an example.

For many usage examples, see the tests directory in the Futhark source directory. A simple example can be found in EXAMPLES below.



The backend used when compiling Futhark programs (without leading futhark, e.g. just opencl).


Only run compiled code - do not run any interpreters.


Compile the programs, but do not run them.


The number of tests to run concurrently. Defaults to the number of (hyper-)cores available.


Do not run test cases that contain the given tag. Cases marked with “disable” are ignored by default.


Only interpret - do not run any compilers.


Type-check the programs, but do not run them.


The program used to perform operations (eg. compilation). Defaults to the binary running futhark test itself.


Print each result on a line by itself, without line buffering.


Do not look for tuning files.


Pass an option to benchmark programs that are being run. For example, we might want to run OpenCL programs on a specific device:

futhark test prog.fut --backend=opencl --pass-option=-dHawaii

Pass an extra option to the compiler when compiling the programs.


If set to a non-empty string, compiled programs are not run directly, but instead the indicated program is run with its first argument being the path to the compiled Futhark program. This is useful for compilation targets that cannot be executed directly (as with futhark-pyopencl on some platforms), or when you wish to run the program on a remote machine.


For each program being run, look for a tuning file with this extension, which is suffixed to the name of the program. For example, given --tuning=tuning (the default), the program foo.fut will be passed the tuning file foo.fut.tuning if it exists.


The following program tests simple indexing and bounds checking:

-- Test simple indexing of an array.
-- ==
-- tags { firsttag secondtag }
-- input { [4,3,2,1] 1 }
-- output { 3 }
-- input { [4,3,2,1] 5 }
-- error: Assertion.*failed

let main (a: []i32) (i: i32): i32 =

The following program contains two entry points, both of which are tested:

let add(x: i32, y: i32): i32 = x + y

-- Test the add1 function.
-- ==
-- entry: add1
-- input { 1 } output { 2 }

entry add1 (x: i32): i32 = add x 1

-- Test the sub1 function.
-- ==
-- entry: sub1
-- input { 1 } output { 0 }

entry sub1 (x: i32): i32 = add x (-1)

The following program contains an entry point that is tested with randomly generated data:

-- ==
-- random input { [100]i32 [100]i32 } auto output
-- random input { [1000]i32 [1000]i32 } auto output

let main xs ys = i32.product (map2 (*) xs ys)