Test for #237 + some more tests for format

The previous commit and its refactoring already "accidentally"
fixed the bug as it removed the faulty duration_output and
substituted it with the existing memory_output that already that
takes care of this case.

lib/benchee/conversion/format.ex

@@ -40,6 +40,10 @@ defmodule Benchee.Conversion.Format do
   custom separator string that will appear between the value and label in the
   formatted output. If no `separator/0` function exists, the default separator
   (a single space) will be used.
+
+      iex> Benchee.Conversion.Format.format({1.0, :kilobyte}, Benchee.Conversion.Memory)
+      "1 KB"
+
   """
   def format({count, unit = %Unit{}}) do
     format(count, label(unit), separator())
@@ -59,12 +63,6 @@ defmodule Benchee.Conversion.Format do
     |> format
   end
 
-  def format(number) do
-    number
-    |> Scale.scale()
-    |> format()
-  end
-
   @default_separator " "
   # should we need it again, a customer separator could be returned
   # per module here

lib/benchee/formatters/console/helpers.ex

@@ -4,7 +4,7 @@ defmodule Benchee.Formatters.Console.Helpers do
   memory usage statistics.
   """
 
-  alias Benchee.Conversion.{Count, DeviationPercent, Duration, Format, Scale, Unit}
+  alias Benchee.Conversion.{Count, DeviationPercent, Format, Scale, Unit}
   alias Benchee.Statistics
 
   @type unit_per_statistic :: %{atom => Unit.t()}

test/benchee/formatters/console/memory_test.exs

@@ -378,6 +378,41 @@ defmodule Benchee.Formatters.Console.MemoryTest do
       assert output =~ "Second"
       refute output =~ "x memory usage"
     end
+
+    test "it doesn't blow up if some come back with a median et. al. of nil" do
+      scenarios = [
+        %Scenario{
+          name: "First",
+          memory_usage_statistics: %Statistics{},
+          run_time_statistics: %Statistics{}
+        },
+        %Scenario{
+          name: "Second",
+          memory_usage_statistics: %Statistics{
+            average: 100.0,
+            median: 100.0,
+            sample_size: 5,
+            percentiles: %{99 => 100.0},
+            std_dev: 5.0,
+            std_dev_ratio: 0.10
+          },
+          run_time_statistics: %Statistics{}
+        }
+      ]
+
+      output =
+        Enum.join(
+          Memory.format_scenarios(scenarios, %{
+            comparison: true,
+            unit_scaling: :best,
+            extended_statistics: false
+          })
+        )
+
+      assert output =~ "First"
+      assert output =~ "Second"
+      refute output =~ "x memory usage"
+    end
   end
 
   defp assert_column_width(name, string, expected_width) do