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Use Sorbet compatible setup-initializations in tests

Sorbet can help with type inference in tests if the setup is right. Otherwise types will be reduced to T.untyped.

Don't do

class Test < ActiveSupport::TestCase
  def setup # Don't use `dev setup`.
 @user = make_fixture(User, :alex) # Don't forget `T.let`

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Tip for test mock builders for denormalized attributes

(This is just one recommendation - and doesn't talk about error-free data structure design.)

Let's say there is a Project class that needs a convenience builder for testing. This Project consist of a company who owns the project and a list of tickets - where a ticket is just a name and the same company denormalized (for reasons). Since this company attribute is just a denormalization - it is/must-be consistent.

Don't do

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/*
 * The task is to write a ~Java~ Rust program which reads the file, calculates the
 * min, mean, and max temperature value per weather station, and emits the results
 * on stdout like this (i.e. sorted alphabetically by station name, and the result
 * values per station in the format <min>/<mean>/<max>, rounded to one fractional digit):
 *
 * {
 *  Abha=-23.0/18.0/59.2,
 *  Abidjan=-16.2/26.0/67.3,
 *  Abéché=-10.0/29.4/69.0,

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# Terminal Tetris
#
# Usage:
#
# ```bash
# ruby tetris.rb <WIDTH> <HEIGHT> <SPEED>
# ```
#
# Control:
# - a: left

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note = File.read(ARGV[0])

gid = 1
prev_indent = 0
stack = [0]

labels = ["Root"]
edges = []

note.lines.map { _1.delete!("\n") }.map do |line|

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IO#reopen and its surprising side effect

This is a short debugging story that led to a few learnings. Our team is working on making TruffleRuby support one of our larger internal Ruby application. Running tests in CI we've noticed a flaky test failure reporting:

undefined method 'write_without_cli_ui' for #<IO:<STDOUT>> (NoMethodError)

Debugging

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#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

#define PIPE_MAX (1 << 16)

int main() {
	int pipefd[2];

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=begin

Extracts a block of subtree from a callgraph of a given function (matched by a substring).

Use:

jt ruby --cpusampler=calltree -e 'a=[];a.push(1);p(a.size)' | ruby truffle_calltree_find.rb "IO#puts"

=end

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=begin

WADIS is a Redis variable watcher.

Usage:

```shell
ruby wadis.rb <HOST> <PORT> --hkey=<key1>,<key2>... --vkey=<key1>,<key2>...
```

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require("thread")

class Foo
	def initialize(arr)
		@arr = arr
	end

	def update
		i = @arr[-1]
		@arr.push(i + 1)