PropCheck.forall

You're seeing just the macro forall, go back to PropCheck module for more information.
Link to this macro

forall(binding, opts \\ [:quiet], property)

View Source (macro)

A property that should hold for all values generated.

iex> use PropCheck
iex> quickcheck(
...> forall n <- nat() do
...>   n >= 0
...> end)
true

If you need more than one generator, collect the generator names and the generators definitions in tuples or lists, respectively:

iex> use PropCheck
iex> quickcheck(
...> forall [n, l] <- [nat(), list(nat())] do
...>   n * Enum.sum(l) >= 0
...> end
...>)
true

Similar to let/2, multiple types can also be combined in a list of bindings:

iex> use PropCheck
iex> quickcheck(
...> forall [n <- nat(), l <- list(nat())] do
...>   n * Enum.sum(l) >= 0
...> end
...>)
true

forall allows using ExUnit assertions. By default (:quiet), no output is generated if an assertion does not hold:

iex> use PropCheck
iex> quickcheck(
...> forall n <- nat() do
...>   assert n < 0
...> end
...>)
false

Use :verbose to enable output on failed ExUnit assertions.

Setting Verbosity on the Command Line

Apart from setting :verbose or :quiet explicitly in the source code, the PROPCHECK_VERBOSE environment variable can also be used to set the verbosity. PROPCHECK_VERBOSE=1 sets :verbose, while PROPCHECK_VERBOSE=0 sets :quiet.