power_assert¶ ↑

About¶ ↑

Power Assert shows each value of variables and method calls in the expression. It is useful for testing, providing which value wasn’t correct when the condition is not satisfied.

Failure:
   assert { 3.times.to_a.include?(3) }
              |     |    |
              |     |    false
              |     [0, 1, 2]
              #<Enumerator: 3:times>

In general, you don’t need to use this library directly. Use following test frameworks or extensions instead.

Requirement¶ ↑

CRuby 3.1+

Configuration¶ ↑

To colorize output messages, add require "power_assert/colorize" to your code. (It requires irb 1.3.1+)

Known Limitations¶ ↑

Expressions must be on a single line. Splitting an assertion across multiple lines prevents any report from being generated, e.g.:

assert do
  # Reported
  func(foo: 0123456789, bar: "abcdefg")
end

assert do
  # Not reported
  func(foo: 0123456789,
       bar: "abcdefg")
end

Expressions must include at least one method call. Assertions without method calls generate no report, e.g.:

val = false
assert do
  # Reported
  val == true
end

assert do
  # Not reported
  val
end

Return values from method_missing or super generate no report, e.g.:

class Foo
  def method_missing(*)
    :foo
  end
end
foo = Foo.new

assert do
  # Not reported
  foo.foo
end

Avoid conditional branches inside assertions. Conditional logic may prevent a report from being generated, e.g.:

condition = true
expected = false
actual = true
assert do
  # This fails, but nothing is reported
  condition ? expected == actual : expected == actual
end

(CRuby 4.0+) <Struct subclass>.new generates no report. Use <Struct subclass>.[] instead, e.g.:

s = Struct.new(:a)
assert do
  # Not reported
  s.new(0)
end

assert do
  # Reported
  s[0]
end

Reference¶ ↑

Power Assert in Ruby (at RubyKaigi 2014) // Speaker Deck