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let flag = true;

if (foo === bar) {
  flag = false; 
  console.log(flag); // false
}

console.log(flag); // false

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defmodule EctoValidationsTest do
  @moduledoc """
  I set up these tests to document how some of the built-in Ecto Changeset
  validations work.  It seems as though:
    - If a field is marked as required, no subsequent validation will be done
      when the field is not present in the params.
    - Duplicating validate_required checks does not add duplicate errors, but
      duplicating other types of validations does add duplicate errors.
    - If a field passes its validate_required check, then all subsequent
      validation checks will be run, even if some fail (no early exiting).

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# This is the "top-level" function for my application
def handle_kafka_message(msg) do
  # Try to do the processing
  :ok = process(msg)
  :ok = acknowledge(msg)
  
# Use catch/2 to handle errors, and send message to DLQ
catch kind, error ->
  Datadog.emit("process_message_failure")
  Logger.error("""

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try do
  # code
catch
  kind, value ->
    # ...
end

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@doc """
Asserts that the given changeset is invalid, and that when the
assertion_expression is applied to the error_message it results in a truthy
value.
"""
defmacro assert_invalid(changeset, field, assertion_expression) when is_atom(field) do
  expr = Macro.to_string(assertion_expression)
  quote do
    c = unquote(changeset)

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defmodule Demo do
  use ExUnit.Case
  
  # The macro comes from here
  import TestHelper

  # An example Ecto Schema for us to play around with
  defmodule Person do
    use Ecto.Schema
    alias Ecto.Changeset

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test "age is required" do
  params = %{"name" => "tyler"}
  changset = Person.changeset(%Person{}, params)
  
  assert_invalid changeset, :age, error_message =~ "blank" && error_message =~ "please"
end

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test "age is required" do
  # Create changeset
  params = %{"name" => "tyler"}
  changset = Person.changeset(%Person{}, params)
  
  # Changeset should be invalid
  assert changeset.valid? == false

  # Find the error message for the invalid field
  error_message = Keyword.get(changeset.errors, :age)

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### mix phx.routes

user_path  GET     /users                                 PhoenixPlaygroundWeb.UserController :index
user_path  GET     /users/:id/edit                        PhoenixPlaygroundWeb.UserController :edit
user_path  GET     /users/new                             PhoenixPlaygroundWeb.UserController :new
user_path  GET     /users/:id                             PhoenixPlaygroundWeb.UserController :show
user_path  POST    /users                                 PhoenixPlaygroundWeb.UserController :create
user_path  PATCH   /users/:id                             PhoenixPlaygroundWeb.UserController :update
           PUT     /users/:id                             PhoenixPlaygroundWeb.UserController :update
user_path  DELETE  /users/:id                             PhoenixPlaygroundWeb.UserController :delete