rats "greets the user" result = test.run("./myapp greet World") test.assert_eq(result["status"], 0) test.assert_eq(result["output"], "Hello, World!") end

rats "fails on missing arguments" result = test.run("./myapp greet") test.assert_eq(result["status"], 1) test.assert_contains(result["output"], "missing argument") end

rats "can be skipped" test.skip("not ready yet") end


## CLI

```bash
rugo rats                            # run all _test.rugo files in rats/ (or current dir)
rugo rats test/myapp_test.rugo         # run specific file
rugo rats myapp.rugo                   # run inline tests in a regular .rugo file
rugo rats --filter "greet"           # filter by test name
rugo rats -j 4                       # run with 4 parallel workers
rugo rats -j 1                       # run sequentially
rugo rats --tap                      # raw TAP output
rugo rats --recap                    # Print all failures with details at the end
rugo rats --timing                   # Per test and total elapsed time

Output

$ rugo rats
 ✓ greets the user
 ✓ fails on missing arguments
 ✓ lists files
 - can be skipped (skipped: not ready yet)

4 tests, 3 passed, 0 failed, 1 skipped

TAP mode:

1..4
ok 1 greets the user
ok 2 fails on missing arguments
ok 3 lists files
ok 4 can be skipped # SKIP not ready yet

`test` Stdlib Module

`test.run(cmd)` — Run a command and capture results

Returns a hash with:

"status" — exit code (integer)
"output" — combined stdout+stderr (string)
"lines" — output split by newlines (array)

result = test.run("echo hello")
# result["status"]  → 0
# result["output"]  → "hello"
# result["lines"]   → ["hello"]

Assertions

Function	Description
`test.assert_eq(actual, expected)`	Equal (`==`)
`test.assert_neq(actual, expected)`	Not equal (`!=`)
`test.assert_true(val)`	Truthy
`test.assert_false(val)`	Falsy
`test.assert_contains(str, substr)`	String contains substring
`test.assert_nil(val)`	Value is nil
`test.fail(msg)`	Explicitly fail the test

Flow control

Function	Description
`test.skip(reason)`	Skip the current test

How the Test Runner Works

The rugo rats command:

Discovers _test.rugo files (in rats/ by default, or specified paths)
For each file: a. Parse and find all rats "name" ... end blocks b. Find setup/teardown if defined c. Generate a Go program that:
- Defines each test as a function
- Wraps each test in defer recover() to catch assertion panics
- Calls setup() → test → teardown() for each
- Outputs TAP format results
Compile and run the generated program
Parse output and display results

Assertions use panic() to abort the test on failure — Go's recover() catches them cleanly.

Test Helpers

RATS supports shared helper files via a helpers/ directory next to the test file. Any .rugo files in helpers/ are automatically required into the test file before parsing, so functions and constants defined there are available to all tests without explicit require statements.

my_tests/
  helpers/
    web_utils.rugo      # defines start_server(), etc.
    fixtures.rugo        # defines test data
  feature_test.rugo      # can call start_server() directly

The compiler generates require "helpers/web_utils" as "web_utils" (and so on) for each .rugo file in the directory. Helpers are only loaded in test mode (rugo rats), not during normal rugo run.

Inline Tests

Tests can be embedded directly in regular .rugo files alongside normal code. When run with rugo run, the rats blocks are silently ignored. When run with rugo rats, they execute as tests.

# math.rugo
use "test"

def add(a, b)
  return a + b
end

puts add(2, 3)

# Inline tests — ignored by `rugo run`, executed by `rugo rats`
rats "add returns the sum"
  test.assert_eq(add(1, 2), 3)
  test.assert_eq(add(-1, 1), 0)
end

$ rugo run math.rugo
5

$ rugo rats math.rugo
 ✓ add returns the sum

When scanning a directory, rugo rats discovers both _test.rugo files and regular .rugo files containing rats blocks. Directories named fixtures are skipped during discovery.

Regression Test Suite

The rats/ directory contains the project's regression test suite.

Fixtures live in rats/fixtures/ (.rugo files for scripts, _test.rugo files for test fixtures).

Do's and Don'ts When Writing RATS Tests

DO: Inline code inside `rats` blocks (preferred)

Write assertions directly inside the rats block. This is the cleanest, most readable pattern and should be the default choice.

use "test"
use "re"

rats "variables and arithmetic"
  x = 10
  y = 20
  test.assert_eq(x + y, 30)
end

rats "re.find returns first match"
  test.assert_eq(re.find("\\d+", "abc123def456"), "123")
end

rats "struct constructor"
  p = Point(10, 20)
  test.assert_eq(p.x, 10)
  test.assert_eq(p.y, 20)
end

DO: Define functions and structs outside `rats` blocks

Top-level def functions, struct definitions, use imports, and require imports are visible to all rats blocks in the file. Use this to share helpers across tests.

use "test"

struct Point
  x
  y
end

def Point.sum()
  return self.x + self.y
end

def get_name(obj)
  return obj.name
end

rats "method call"
  p = Point(3, 7)
  test.assert_eq(p.sum(), 10)
end

rats "helper function"
  h = {"name" => "Alice"}
  test.assert_eq(get_name(h), "Alice")
end

DO: Use lambdas inline inside `rats` blocks

Lambda definitions work directly inside rats blocks.

use "test"

rats "type_of lambda"
  f = fn(x) x + 1 end
  test.assert_eq(type_of(f), "Lambda")
end

rats "lambda as callback"
  nums = [1, 2, 3]
  doubled = map(nums, fn(n) n * 2 end)
  test.assert_eq(doubled, [2, 4, 6])
end

DO: Use `eval.run()` with heredocs when inline is not possible

When you need to test error conditions, exit codes, compile errors, pipe chains, or features that require output capture (puts), use the eval module with heredocs. This compiles and runs the snippet in a subprocess.

use "test"
use "eval"

rats "division by zero is a runtime error"
  source = <<~RUGO
    x = 5 / 0
  RUGO
  result = eval.run(source)
  test.assert_neq(result["status"], 0)
  test.assert_contains(result["output"], "division by zero")
end

rats "pipe chain works"
  source = <<~RUGO
    use "str"
    echo "hello world" | str.upper | puts
  RUGO
  result = eval.run(source)
  test.assert_eq(result["status"], 0)
  test.assert_eq(result["output"], "HELLO WORLD")
end

Use single-quoted heredoc delimiters (<<~'RUGO') when the snippet contains string interpolation that should not be expanded by the outer test:

rats "dot access on string is a runtime error"
  source = <<~'RUGO'
    x = "hello"
    puts(x.name)
  RUGO
  result = eval.run(source)
  test.assert_neq(result["status"], 0)
  test.assert_contains(result["output"], "cannot access .name on String")
end

DON'T: Use fixtures and `test.run("rugo run ...")` unless unavoidable

Fixture-based tests that shell out to rugo run rats/fixtures/some_file.rugo are harder to read because the test logic lives in a separate file. Avoid this pattern unless you are testing CLI behavior, binary compilation, or process-level concerns that genuinely require a separate invocation.

Acceptable uses of test.run():

# OK — testing the CLI itself
rats "rugo --version works"
  result = test.run("rugo --version")
  test.assert_eq(result["status"], 0)
  test.assert_contains(result["output"], "rugo version")
end

# OK — testing binary compilation
rats "rugo build creates binary"
  result = test.run("rugo build -o #{test.tmpdir()}/hello examples/hello.rugo")
  test.assert_eq(result["status"], 0)
end

If you find yourself writing test.run("rugo run rats/fixtures/..."), stop and ask: can this be inlined in the rats block, or written with eval.run() and a heredoc? Almost always, yes.

DON'T: Reference top-level variables or constants from inside `rats` blocks

Each rats block is an isolated scope. Top-level variables and constants are not visible inside rats blocks -- the compiler will emit an error.

use "test"

port = 8080     # top-level variable
PORT = 9090     # top-level constant

rats "this will NOT compile"
  # WRONG — port and PORT are not in scope here
  test.assert_eq(port, 8080)   # compile error!
  test.assert_eq(PORT, 9090)   # compile error!
end

What IS shared across rats blocks:

def functions
struct definitions
use module imports
require imports

What is NOT shared:

Variables (lowercase)
Constants (UPPERCASE)
Anything defined inside another rats block

Pattern summary

Pattern	When to use
Inline (preferred)	Value checks, module calls, structs, loops, conditions -- anything testable via direct assertions
eval.run() + heredoc (acceptable)	Error conditions, exit codes, pipe chains, compile errors, features needing `puts` output capture
test.run() + fixtures (avoid)	Only for CLI testing, binary compilation, or process-level behavior that cannot be expressed otherwise

Running RATS

make rats is the canonical way to run the full RATS suite. Always run it before finalizing any work.

When developing, run specific directories or files first for fast feedback, then finish with a single make rats to verify everything passes:

# Fast feedback during development — run specific dirs/files first
bin/rugo rats rats/core/                       # run core language tests
bin/rugo rats rats/stdlib/                     # run stdlib module tests
bin/rugo rats rats/gobridge/                   # run Go bridge tests
bin/rugo rats rats/tools/                      # run tool tests
bin/rugo rats rats/core/03_control_flow_test.rugo  # run a specific test file

# Then run the full suite before calling it done
make rats

New Language Features Required (from design doc)

See docs/rats.md for the full design document including:

Required language features (rats keyword, str module, test runner)
Implementation order
Generated Go code examples
Feature comparison with BATS

rugo-rats

RATS — Rugo Automated Testing System

Test Syntax