Package {muttest}

Type: Package
Title: Mutation Testing
Version: 0.2.0
Description: Measure quality of your tests. 'muttest' introduces small changes (mutations) to your code and runs your tests to check if they catch the changes. If they do, your tests are good. If not, your assertions are not specific enough. 'muttest' gives you percent score of how often your tests catch the changes.
License: MIT + file LICENSE
Encoding: UTF-8
RoxygenNote: 7.3.3
Depends: R (≥ 4.1.0)
Imports: checkmate, cli, fs, mirai, R6, rlang, testthat, treesitter, treesitter.r, withr
Config/testthat/edition: 3
URL: https://jakubsobolewski.com/muttest/
Suggests: box, covr, cucumber (≥ 2.1.0), ggplot2, knitr, purrr, rmarkdown, shiny, stringr
VignetteBuilder: knitr
NeedsCompilation: no
Packaged: 2026-05-14 12:42:50 UTC; jakubsobolewski
Author: Jakub Sobolewski [aut, cre]
Maintainer: Jakub Sobolewski <jakupsob@gmail.com>
Repository: CRAN
Date/Publication: 2026-05-14 14:20:02 UTC

CopyStrategy interface

Description

Extend this class to implement a custom copy strategy.

Methods

Public methods

Method execute()

Copy project files according to the strategy

Usage
CopyStrategy$execute(original_dir)
Arguments
original_dir

The original directory to copy from

plan

The current test plan

Returns

The path to the temporary directory

Method clone()

The objects of this class are cloneable with this method.

Usage
CopyStrategy$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other CopyStrategy: PackageCopyStrategy, default_copy_strategy()

Run tests matching the mutated source file name

Description

This strategy tells if a mutant is caught by a test matching the source file name.

For example, if the source file name is foo.R, and there are test files named test-foo.R or test-bar.R, only test-foo.R will be run.

This strategy should give faster results than ?FullTestStrategy, especially for big codebases, but the score might be less accurate.

Super class

muttest::TestStrategy -> FileTestStrategy

Methods

Public methods

Method new()

Initialize the FileTestStrategy

Usage
FileTestStrategy$new(
  load_helpers = TRUE,
  load_package = c("source", "none", "installed")
)
Arguments
load_helpers

Whether to load test helpers

load_package

The package loading strategy

Method execute()

Execute the test strategy

Usage
FileTestStrategy$execute(path, plan, reporter)
Arguments
path

The path to the test directory

plan

The current mutation plan. See muttest_plan().

reporter

The reporter to use for test results

Returns

The test results

Method clone()

The objects of this class are cloneable with this method.

Usage
FileTestStrategy$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other TestStrategy: FullTestStrategy, TestStrategy, default_test_strategy()

Run all tests for a mutant

Description

This test strategy tells if a mutant is caught by any test.

To get faster results, especially for big codebases, use ?FileTestStrategy instead.

Super class

muttest::TestStrategy -> FullTestStrategy

Methods

Public methods

Method new()

Initialize

Usage
FullTestStrategy$new(
  load_helpers = TRUE,
  load_package = c("source", "none", "installed")
)
Arguments
load_helpers

Whether to load test helpers

load_package

The package loading strategy

Method execute()

Execute the test strategy

Usage
FullTestStrategy$execute(path, plan, reporter)
Arguments
path

The path to the test directory

plan

The current mutation plan. See muttest_plan().

reporter

The reporter to use for test results

Returns

The test results

Method clone()

The objects of this class are cloneable with this method.

Usage
FullTestStrategy$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other TestStrategy: FileTestStrategy, TestStrategy, default_test_strategy()

Reporter for Mutation Testing

Description

The job of a mutation reporter is to aggregate and display the results of mutation tests. It tracks each mutation attempt, reporting on whether the tests killed the mutation or the mutation survived.

Public fields

test_reporter

Reporter to use for the testthat::test_dir function

out

Output destination for reporter messages

width

Width of the console in characters

unicode

Whether Unicode output is supported

crayon

Whether colored output is supported

rstudio

Whether running in RStudio

hyperlinks

Whether terminal hyperlinks are supported

current_file

Path of the file currently being mutated

current_mutator

Mutator currently being applied

plan

Complete mutation plan for the test run

results

List of mutation test results, indexed by file path

current_score

Current score of the mutation tests

error_messages

List of error messages from failed mutant runs

Methods

Public methods

Method new()

Initialize a new reporter

Usage
MutationReporter$new(test_reporter = "silent", file = stdout())
Arguments
test_reporter

Reporter to use for the testthat::test_dir function

file

Output destination (default: stdout)

Method start_reporter()

Start reporter

Usage
MutationReporter$start_reporter(plan = NULL)
Arguments
plan

The complete mutation plan

temp_dir

Path to the temporary directory for testing

Method start_file()

Start testing a file

Usage
MutationReporter$start_file(filename)
Arguments
filename

Path to the file being mutated

Method start_mutator()

Start testing with a specific mutator

Usage
MutationReporter$start_mutator(mutator)
Arguments
mutator

The mutator being applied

Method add_result()

Add a mutation test result

Usage
MutationReporter$add_result(
  plan,
  killed,
  survived,
  errors,
  error = NULL,
  original_code = NULL,
  mutated_code = NULL
)
Arguments
plan

Current testing plan. See muttest_plan().

killed

Whether the mutation was killed by tests

survived

Number of survived mutations

errors

Number of errors encountered

error

Optional error condition from a failed run

original_code

Original source lines before mutation

mutated_code

Mutated source lines

Method update()

Update status (no-op in base class)

Usage
MutationReporter$update(force = FALSE)
Arguments
force

Ignored

Method end_mutator()

End testing with current mutator

Usage
MutationReporter$end_mutator()

Method end_file()

End testing current file

Usage
MutationReporter$end_file()

Method end_reporter()

End reporter and show summary

Usage
MutationReporter$end_reporter()

Method get_score()

Get the current score

Usage
MutationReporter$get_score()

Method cat_tight()

Print a message to the output

Usage
MutationReporter$cat_tight(...)
Arguments
...

Message to print

Method cat_line()

Print a message to the output

Usage
MutationReporter$cat_line(...)
Arguments
...

Message to print

Method rule()

Print a message to the output with a rule

Usage
MutationReporter$rule(...)
Arguments
...

Message to print

Method clone()

The objects of this class are cloneable with this method.

Usage
MutationReporter$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other MutationReporter: ProgressMutationReporter, default_reporter()

Mutator

Description

Mutator

Mutator

Details

Represents a single code mutation — a pattern to find and a replacement to apply. Every mutator function (operator(), boolean_literal(), etc.) returns an instance of this class.

Public fields

from

The token or operator to replace.

to

The replacement token or operator.

query

Tree-sitter query used to locate candidate nodes.

match_fn

Optional ⁠function(node_text)⁠ returning logical; overrides the default node_text == from equality check.

replacement_fn

Optional ⁠function(node_text)⁠ returning a string; overrides the static to value as the replacement text.

mutate_fn

Optional ⁠function(code)⁠ that fully replaces the default mutation logic when set.

Methods

Public methods

Method new()

Create a new Mutator.

Usage
Mutator$new(
  from,
  to,
  query,
  match_fn = NULL,
  replacement_fn = NULL,
  mutate_fn = NULL
)
Arguments
from

Token to replace.

to

Replacement token.

query

Tree-sitter query string.

match_fn

Optional custom match function.

replacement_fn

Optional custom replacement function.

mutate_fn

Optional ⁠function(code)⁠ that fully overrides the default mutation logic.

Method mutate()

Apply this mutator to a character vector of source lines.

Usage
Mutator$mutate(code)
Arguments
code

Character vector of source lines.

Returns

A list of mutated code variants (one per match), or NULL if the pattern was not found.

Method print()

Print a short summary of the mutator.

Usage
Mutator$print()

Method clone()

The objects of this class are cloneable with this method.

Usage
Mutator$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

Package copy strategy

Description

It copies all files and directories from the original directory to a temporary directory.

Super class

muttest::CopyStrategy -> PackageCopyStrategy

Methods

Public methods

Method execute()

Copy project files, excluding hidden and temp directories

Usage
PackageCopyStrategy$execute(original_dir, plan)
Arguments
original_dir

The original directory to copy from

plan

The current test plan

Returns

The path to the temporary directory

Method clone()

The objects of this class are cloneable with this method.

Usage
PackageCopyStrategy$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other CopyStrategy: CopyStrategy, default_copy_strategy()

Progress Reporter for Mutation Testing

Description

A reporter that displays a progress indicator for mutation tests. It provides real-time feedback on which mutants are being tested and whether they were killed by tests.

Super class

muttest::MutationReporter -> ProgressMutationReporter

Public fields

start_time

Time when testing started (for duration calculation)

min_time

Minimum test duration to display timing information

col_config

List of column configuration for report formatting

survived_detail

Controls how survived mutants are reported (summary, none)

survived_mutants

List to store details of survived mutants for summary reporting

Methods

Public methods

Inherited methods

Method format_column()

Format a column with specified padding and width

Usage
ProgressMutationReporter$format_column(text, col_name, colorize = NULL)
Arguments
text

Text to format

col_name

Column name to use configuration from

colorize

Optional function to color the text

Method fmt_h()

Format the header of the report

Usage
ProgressMutationReporter$fmt_h()

Method fmt_r()

Format a row of the report

Usage
ProgressMutationReporter$fmt_r(status, k, s, e, t, score, mutator, file)
Arguments
status

Status symbol (e.g., tick or cross)

k

Number of killed mutations

s

Number of survived mutations

e

Number of errors

t

Total number of mutations

score

Score percentage

mutator

The mutator used

file

The file being tested

Returns

Formatted row string

Method new()

Initialize a new progress reporter

Usage
ProgressMutationReporter$new(
  test_reporter = "silent",
  min_time = 1,
  file = stdout(),
  survived_detail = c("summary", "none")
)
Arguments
test_reporter

Reporter to use for testthat::test_dir

min_time

Minimum time to show elapsed time (default: 1s)

file

Output destination (default: stdout)

survived_detail

Controls how survived mutants are reported. One of "summary" (default) or "none".

Method start_reporter()

Start reporter

Usage
ProgressMutationReporter$start_reporter(plan = NULL)
Arguments
plan

The complete mutation plan

Method add_result()

Add a mutation test result

Usage
ProgressMutationReporter$add_result(
  plan,
  killed,
  survived,
  errors,
  error = NULL,
  original_code = NULL,
  mutated_code = NULL
)
Arguments
plan

Current testing plan. See muttest_plan().

killed

Whether the mutation was killed by tests

survived

Number of survived mutations

errors

Number of errors encountered

error

Optional error condition from a failed run

original_code

Original source lines before mutation

mutated_code

Mutated source lines

Method update()

Update status spinner (for long-running operations)

Usage
ProgressMutationReporter$update(force = FALSE)
Arguments
force

Force update even if interval hasn't elapsed

Method end_file()

End testing current file

Usage
ProgressMutationReporter$end_file()

Method cr()

Carriage return if dynamic, newline otherwise

Usage
ProgressMutationReporter$cr()

Method end_reporter()

End reporter with detailed summary

Usage
ProgressMutationReporter$end_reporter()

Method print()

Print the mutation test result with survived diffs

Usage
ProgressMutationReporter$print()

Method clone()

The objects of this class are cloneable with this method.

Usage
ProgressMutationReporter$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other MutationReporter: MutationReporter, default_reporter()

TestStrategy interface

Description

Extend this class to implement a custom test strategy.

Methods

Public methods

Method execute()

Execute the test strategy

Usage
TestStrategy$execute(path, plan, reporter)
Arguments
path

The path to the test directory

plan

The current mutation plan. See muttest_plan().

reporter

The reporter to use for test results

Returns

The test result

Method clone()

The objects of this class are cloneable with this method.

Usage
TestStrategy$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

See Also

Other TestStrategy: FileTestStrategy, FullTestStrategy, default_test_strategy()

Arithmetic operator mutators

Description

Returns a ready-made list of operator() mutators covering common arithmetic swaps: +/-, *//, ^/*, %%/*, %/%//.

Usage

arithmetic_operators()

Details

Use on any file that performs calculations. A surviving mutant from this preset typically means an assertion checks a property of the result (sign, order) rather than a specific value — replacing expect_gte() with expect_equal() and a computed expected value usually kills it.

Value

A list of operator() mutators.

See Also

vignette("mutators", package = "muttest") for the full operator table and a worked example showing the direction-insensitive assertion pattern.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

arithmetic_operators()

## Not run: 
plan <- muttest_plan(
  source_files = "R/stats.R",
  mutators = arithmetic_operators()
)
muttest(plan, "tests/testthat")

## End(Not run)

Mutate a boolean literal

Description

Replaces a boolean constant (TRUE, FALSE, T, or F) with another one.

Usage

boolean_literal(from, to)

Arguments

from

The literal to be replaced. One of "TRUE", "FALSE", "T", "F".

to

The literal to replace with.

Examples

boolean_literal("TRUE", "FALSE")
boolean_literal("FALSE", "TRUE")
boolean_literal("T", "F")
boolean_literal("F", "T")

Boolean literal mutators

Description

Returns a ready-made list of boolean_literal() mutators covering all canonical flips: TRUE/FALSE and T/F.

Usage

boolean_literals()

Details

Use on any file that passes or returns boolean flags. A surviving mutant from this preset typically means a test checks a side effect of the flag (e.g. the branch taken) rather than the flag value itself — adding expect_true()/expect_false() on the return value kills it.

Value

A list of boolean_literal() mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

boolean_literals()

## Not run: 
plan <- muttest_plan(
  source_files = "R/flags.R",
  mutators = boolean_literals()
)
muttest(plan, "tests/testthat")

## End(Not run)

Mutate a function call name

Description

Replaces a function name in a call expression with another name. Useful for swapping semantically related functions such as any/all, min/max, or sum/prod.

Usage

call_name(from, to)

Arguments

from

The function name to replace.

to

The function name to replace with.

Examples

call_name("any", "all")
call_name("min", "max")
call_name("sum", "prod")

Comparison operator mutators

Description

Returns a ready-made list of operator() mutators covering direction swaps (</>, <=/>=, ==/!=) and boundary shifts (</<=, >/>=).

Usage

comparison_operators()

Details

Use on any file with threshold logic, range checks, or filter conditions. A surviving mutant from this preset means the exact boundary value implied by the operator was never passed to the function — adding a test at that boundary value kills it.

Value

A list of operator() mutators.

See Also

vignette("mutators", package = "muttest") for the full operator table and a worked example showing the missing boundary value pattern.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

comparison_operators()

## Not run: 
plan <- muttest_plan(
  source_files = "R/shipping.R",
  mutators = comparison_operators()
)
muttest(plan, "tests/testthat")

## End(Not run)

Condition mutation mutators

Description

Returns a ready-made list of negate_condition() and remove_condition_negation() mutators covering both directions of condition logic: wrapping a plain condition in !(...) and stripping ! from an already-negated condition.

Usage

condition_mutations()

Details

Use on any file with non-trivial if/while conditions. Surviving mutants mean the branch outcome was never tested with inputs that cross the boundary — adding a test where the condition flips from TRUE to FALSE kills them.

Value

A list of mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

condition_mutations()

## Not run: 
plan <- muttest_plan(
  source_files = "R/validation.R",
  mutators = condition_mutations()
)
muttest(plan, "tests/testthat")

## End(Not run)

Create a default project copy strategy

Description

Create a default project copy strategy

Usage

default_copy_strategy(...)

Arguments

...

Arguments passed to the ?PackageCopyStrategy constructor.

Value

A ?CopyStrategy object

See Also

Other CopyStrategy: CopyStrategy, PackageCopyStrategy

Create a default reporter

Description

Create a default reporter

Usage

default_reporter(...)

Arguments

...

Arguments passed to the ?ProgressMutationReporter constructor.

See Also

Other MutationReporter: MutationReporter, ProgressMutationReporter

Create a default run strategy

Description

Create a default run strategy

Usage

default_test_strategy(...)

Arguments

...

Arguments passed to the ?FullTestStrategy constructor.

Value

A ?TestStrategy object

See Also

Other TestStrategy: FileTestStrategy, FullTestStrategy, TestStrategy

Delete statements one at a time

Description

Produces one mutant per deletable statement, removing each x <- expr assignment or standalone f(...) call from the source. Surviving mutants reveal untested side effects or dead assignments.

Usage

delete_statement()

Details

Function definitions (x <- function(...) { ... }) are left untouched to avoid producing structurally broken mutants.

Value

A Mutator object.

Examples

delete_statement()

Decrement subscript indices

Description

Replaces every simple subscript index in x[i] or x[[i]] with x[i - 1L] / x[[i - 1L]]. Targets identifier and numeric literal indices; complex expressions (e.g. x[a + b]) are left untouched.

Usage

index_decrement()

Value

A Mutator object.

Examples

index_decrement()

Increment subscript indices

Description

Replaces every simple subscript index in x[i] or x[[i]] with x[i + 1L] / x[[i + 1L]]. Targets identifier and numeric literal indices; complex expressions (e.g. x[a + b]) are left untouched.

Usage

index_increment()

Details

Catches off-by-one errors where tests never verify the exact element retrieved from a vector or list.

Value

A Mutator object.

Examples

index_increment()

Index mutation mutators

Description

Returns a ready-made list of index_increment() and index_decrement() mutators that shift every simple subscript index by 1.

Usage

index_mutations()

Details

Use on any file that extracts elements from vectors or lists by position. Surviving mutants reveal off-by-one errors where tests only verify that something was extracted, not which element — asserting the exact value of the extracted element kills them.

Value

A list of mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

index_mutations()

## Not run: 
plan <- muttest_plan(
  source_files = "R/selectors.R",
  mutators = index_mutations()
)
muttest(plan, "tests/testthat")

## End(Not run)

Logical operator mutators

Description

Returns a ready-made list of operator() mutators covering short-circuit (&&/||) and vectorised (&/|) logical operator swaps.

Usage

logical_operators()

Details

Use on any file with compound conditions (⁠if (a && b)⁠). A surviving mutant from this preset typically means test inputs are symmetric — both flags TRUE or both FALSE. Adding a test with one flag TRUE and the other FALSE exposes the difference between && and || and kills the mutant.

Value

A list of operator() mutators.

See Also

vignette("mutators", package = "muttest") for the full operator table and a worked example showing the symmetric-input pattern.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

logical_operators()

## Not run: 
plan <- muttest_plan(
  source_files = "R/access.R",
  mutators = logical_operators()
)
muttest(plan, "tests/testthat")

## End(Not run)

Run a mutation test

Description

Run a mutation test

Usage

muttest(
  plan,
  path = "tests/testthat",
  reporter = default_reporter(),
  test_strategy = default_test_strategy(),
  copy_strategy = default_copy_strategy(),
  workers = 1,
  timeout = 600 * 1000
)

Arguments

plan

A mutation testing plan. See muttest_plan().

path

Path to the test directory.

reporter

Reporter to use for mutation testing results. See ?MutationReporter.

test_strategy

Strategy for running tests. See ?TestStrategy. The purpose of test strategy is to control how tests are executed. We can run all tests for each mutant, or only tests that are relevant to the mutant.

copy_strategy

Strategy for copying the project. See ?CopyStrategy. This strategy controls which files are copied to the temporary directory, where the tests are run.

workers

Number of parallel workers. When greater than 1, mutants are tested concurrently using mirai daemons. Defaults to 1 (sequential).

timeout

Per-mutant timeout in milliseconds. If a mutant's test run exceeds this limit the daemon is interrupted and the result is recorded as an error. Use Inf to disable. Defaults to 600000 (10 minutes).

Value

An object of class muttest_result containing the overall mutation score.

Create a plan for mutation testing

Description

Each mutant requires rerunning the tests. For large project it might be not feasible to test all mutants in one go. This function allows you to create a plan for selected source files and mutators.

Usage

muttest_plan(mutators, source_files = fs::dir_ls("R", regexp = ".[rR]$"))

Arguments

mutators

A list of mutators to use. See operator().

source_files

A vector of file paths to the source files.

Details

The plan is in a data frame format, where each row represents a mutant.

You can subset the plan before passing it to the muttest() function.

Value

A data frame with the test plan. The data frame has the following columns:

Mutate an NA or NULL literal

Description

Replaces NA, NULL, or a typed NA constant (NA_real_, NA_integer_, NA_complex_, NA_character_) with another value.

Usage

na_literal(from, to)

Arguments

from

The literal to replace. One of "NA", "NULL", "NA_real_", "NA_integer_", "NA_complex_", "NA_character_".

to

The replacement literal.

Details

In tree-sitter-r, NA and all typed NA variants share the same na node type, while NULL has its own null node type. match_fn distinguishes between them by comparing the literal text.

Value

A Mutator object.

Examples

na_literal("NULL", "NA")
na_literal("NA", "NULL")
na_literal("NA", "NA_real_")
na_literal("NA_real_", "NA")

NA and NULL literal mutators

Description

Returns a ready-made list of na_literal() mutators covering common swaps between NA, NULL, and the typed NA variants (NA_real_, NA_integer_, NA_character_).

Usage

na_literals()

Details

Use on any file that handles missing values or nullable results. A surviving mutant typically means tests never distinguish NA from NULL, or never check which typed NA is returned — adding expect_true(is.na(x)) and expect_equal(class(x), "numeric") style assertions kills it.

Value

A list of na_literal() mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

na_literals()

## Not run: 
plan <- muttest_plan(
  source_files = "R/missing.R",
  mutators = na_literals()
)
muttest(plan, "tests/testthat")

## End(Not run)

Negate the condition of if/while statements

Description

Wraps the condition expression of each matching statement in !(...). For example, ⁠if (x > 0)⁠ becomes ⁠if (!(x > 0))⁠.

Usage

negate_condition(statements = c("if", "while"))

Arguments

statements

Character vector of statement types to target. Must be a subset of c("if", "while"). Defaults to both.

Value

A Mutator object.

Examples

negate_condition()
negate_condition(statements = "if")

Decrement numeric literals

Description

Replaces every numeric literal n with n - by. Handles both integer (e.g. 5L) and floating-point (e.g. 3.14) literals.

Usage

numeric_decrement(by = 1)

Arguments

by

The amount to subtract. Defaults to 1.

Value

A Mutator object.

Examples

numeric_decrement()
numeric_decrement(by = 2)

Increment numeric literals

Description

Replaces every numeric literal n with n + by. Handles both integer (e.g. 5L) and floating-point (e.g. 3.14) literals.

Usage

numeric_increment(by = 1)

Arguments

by

The amount to add. Defaults to 1.

Value

A Mutator object.

Examples

numeric_increment()
numeric_increment(by = 2)

Numeric literal mutators

Description

Returns a ready-made list of numeric_increment() and numeric_decrement() mutators that shift every numeric literal by 1.

Usage

numeric_literals()

Details

Use on any file with numeric constants used as thresholds, counts, or offsets. A surviving mutant means tests never verify the exact value of the constant — asserting the precise numeric result rather than a property (e.g. sign) kills it.

Value

A list of mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

numeric_literals()

## Not run: 
plan <- muttest_plan(
  source_files = "R/thresholds.R",
  mutators = numeric_literals()
)
muttest(plan, "tests/testthat")

## End(Not run)

Mutate a binary operator

Description

Produces one mutant per occurrence of from in the source file, replacing it with to. A surviving mutant means your tests cannot distinguish the original operator from the replacement — pointing at the missing assertion or input value.

Usage

operator(from, to)

Arguments

from

The operator to replace (e.g. "+", "==", ">").

to

The replacement operator.

Details

Use this when you need a specific swap not covered by the preset collections (arithmetic_operators(), comparison_operators(), logical_operators()).

Value

A Mutator object.

See Also

comparison_operators(), arithmetic_operators(), logical_operators() for ready-made preset lists.

vignette("mutators", package = "muttest") for the full operator reference with examples of what each preset catches.

vignette("interpreting-results", package = "muttest") to learn how to read surviving mutants and strengthen the tests they expose.

Examples

operator("+", "-")
operator("==", "!=")
operator(">", ">=")  # probe the strict vs. non-strict boundary

Remove negation from the condition of if/while statements

Description

The inverse of negate_condition(). Strips the leading ! from any already-negated condition, so ⁠if (!done)⁠ becomes ⁠if (done)⁠ and ⁠while (!ready)⁠ becomes ⁠while (ready)⁠.

Usage

remove_condition_negation(statements = c("if", "while"))

Arguments

statements

Character vector of statement types to target. Must be a subset of c("if", "while"). Defaults to both.

Details

Unlike remove_negation(), this mutator is scoped exclusively to conditions, leaving negations in other positions (assignments, return values, etc.) untouched.

Value

A Mutator object.

Examples

remove_condition_negation()
remove_condition_negation(statements = "while")

Remove logical negation

Description

Removes the ! unary operator from an expression. For example, !is.na(x) becomes is.na(x) and !(a > b) becomes (a > b).

Usage

remove_negation()

Value

A Mutator object.

Examples

remove_negation()

Replace the value in explicit return() calls

Description

Replaces the argument of every return(expr) with a fixed value (default "NULL"). Tests that only check that a function returns something without asserting the value will not kill these mutants.

Usage

replace_return_value(replacement = "NULL")

Arguments

replacement

Raw R source text to substitute as the return value. Defaults to "NULL". Examples: "NA" inserts the missing value NA; '"NULL"' (inner quotes) inserts the string "NULL"; '"NA"' inserts the string "NA" rather than the missing value.

Details

Only explicit return() calls are targeted. Implicit returns (the last expression of a function body) are not affected.

Value

A Mutator object.

Examples

replace_return_value()
replace_return_value("NA")

Mutate non-empty string literals to the empty string

Description

Replaces any non-empty string literal in the source code with "". The empty string itself is not mutated (use string_fill() for that).

Usage

string_empty()

Value

A Mutator object.

Examples

string_empty()

Mutate the empty string literal to a placeholder string

Description

Replaces "" with a fill string (default "mutant") so that code paths that depend on an empty string can be detected.

Usage

string_fill(fill = "mutant")

Arguments

fill

The replacement string. Defaults to "mutant". Override when the codebase already contains "mutant" as a meaningful value.

Value

A Mutator object.

Examples

string_fill()
string_fill(fill = "PLACEHOLDER")

String literal mutators

Description

Returns a ready-made list of string_empty() and string_fill() mutators covering both directions: collapsing non-empty strings to "" and filling empty strings with a placeholder.

Usage

string_literals()

Details

Use on any file where string values are passed to downstream logic or returned to callers. Surviving mutants reveal tests that only check type or length — asserting the exact string content kills them.

Value

A list of mutators.

See Also

vignette("mutators", package = "muttest") for the full mutator table.

vignette("interpreting-results", package = "muttest") for how to diagnose survivors and fix the underlying test weakness.

Examples

string_literals()

## Not run: 
plan <- muttest_plan(
  source_files = "R/labels.R",
  mutators = string_literals()
)
muttest(plan, "tests/testthat")

## End(Not run)