Simplify fix and test

lib/capybara/server.rb

@@ -105,23 +105,20 @@ module Capybara
     end
 
     def find_available_port(host)
-      port = 0
-      while port.zero?
-        begin
-          server = TCPServer.new(host, port)
-          port = server.addr[1]
-        ensure
-          server&.close
-        end
-        begin
-          server = TCPServer.new(host, port)
-        rescue Errno::EADDRINUSE
-          port = 0
-        ensure
-          server&.close
-        end
-      end
+      server = TCPServer.new(host, 0)
+      port = server.addr[1]
+      server.close
+
+      # Workaround issue where some platforms (mac, ???) when passed a host
+      # of '0.0.0.0' will return a port that is only available on one of the
+      # ip addresses that resolves to, but the next binding to that port requires
+      # that port to be available on all ips
+      server = TCPServer.new(host, port)
       port
+    rescue Errno::EADDRINUSE
+      retry
+    ensure
+      server&.close
     end
   end
 end

spec/server_spec.rb

@@ -74,19 +74,26 @@ RSpec.describe Capybara::Server do
     end
   end
 
-  def use_port(host, port)
-    server = TCPServer.new(host, port)
-  ensure
-    server&.close
-  end
-
   it 'should handle that getting available ports fails randomly' do
-    expect do
-      100000.times do
-        port = described_class.new(Object.new).send(:find_available_port, '0.0.0.0')
-        use_port('0.0.0.0', port)
+    begin
+      # Use a port to force a EADDRINUSE error to be generated
+      server = TCPServer.new('0.0.0.0', 0)
+      server_port = server.addr[1]
+      d_server = instance_double('TCPServer', addr: [nil, server_port, nil, nil], close: nil)
+      call_count = 0
+      allow(TCPServer).to receive(:new).and_wrap_original do |m, *args|
+        begin
+          call_count.zero? ? d_server : m.call(*args)
+        ensure
+          call_count += 1
+        end
       end
-    end.not_to raise_error
+
+      port = described_class.new(Object.new, host: '0.0.0.0').port
+      expect(port).not_to eq(server_port)
+    ensure
+      server&.close
+    end
   end
 
   it 'should return its #base_url' do