Switch test suite to RSpec

Removes Bacon and Mocha

Reasoning explained in this comment: https://github.com/pry/pry/issues/277#issuecomment-51708712

Mostly this went smoothly. There were a few errors that I fixed along
the way, e.g. tests that were failing but for various reasons still
passed. Should have documented them, but didn't think about it until
very near the end. But generaly, I remember 2 reasons this would happen:
`lambda { raise "omg" }.should.raise(RuntimeError, /not-omg/)` will pass
because the second argument is ignored by Bacon. And `1.should == 2`
will return false instead of raising an error when it is not in an it
block (e.g. if stuck in a describe block, that would just return false)

The only one that I felt unsure about was spec/helpers/table_spec.rb
`Pry::Helpers.tablify_or_one_line('head', %w(ing)).should == 'head: ing'`
This is wrong, but was not failing because it was in a describe block
instead of an it block.  In reality, it returns `"head: ing\n"`,
I updated the test to reflect this, though I don't know for sure
this is the right thing to do

This will fail on master until https://github.com/pry/pry/pull/1281 is merged.
This makes https://github.com/pry/pry/pull/1278 unnecessary.

spec/command_set_spec.rb

@@ -15,16 +15,16 @@ describe Pry::CommandSet do
 
   describe "[]=" do
     it "removes a command from the command set" do
-      @set["help"].should.not == nil
+      @set["help"].should_not == nil
       @set["help"] = nil
       @set["help"].should == nil
-      lambda { @set.run_command(TOPLEVEL_BINDING, "help") }.should.raise Pry::NoCommandError
+      expect { @set.run_command(TOPLEVEL_BINDING, "help") }.to raise_error Pry::NoCommandError
     end
 
     it "replaces a command" do
       old_help = @set["help"]
       @set["help"] = @set["pry-version"]
-      @set["help"].should.not == old_help
+      @set["help"].should_not == old_help
     end
 
     it "rebinds the command with key" do
@@ -33,7 +33,7 @@ describe Pry::CommandSet do
     end
 
     it "raises a TypeError when command is not a subclass of Pry::Command" do
-      lambda { @set["help"] = "hello" }.should.raise TypeError
+      expect { @set["help"] = "hello" }.to raise_error TypeError
     end
   end
 
@@ -67,27 +67,21 @@ describe Pry::CommandSet do
 
   it 'should raise an error when calling an undefined command' do
     @set.command('foo') {}
-    lambda {
-      @set.run_command @ctx, 'bar'
-    }.should.raise(Pry::NoCommandError)
+    expect { @set.run_command @ctx, 'bar' }.to raise_error Pry::NoCommandError
   end
 
   it 'should be able to remove its own commands' do
     @set.command('foo') {}
     @set.delete 'foo'
 
-    lambda {
-      @set.run_command @ctx, 'foo'
-    }.should.raise(Pry::NoCommandError)
+    expect { @set.run_command @ctx, 'foo' }.to raise_error Pry::NoCommandError
   end
 
   it 'should be able to remove its own commands, by listing name' do
     @set.command(/^foo1/, 'desc', :listing => 'foo') {}
     @set.delete 'foo'
 
-    lambda {
-      @set.run_command @ctx, /^foo1/
-    }.should.raise(Pry::NoCommandError)
+    expect { @set.run_command @ctx, /^foo1/ }.to raise_error Pry::NoCommandError
   end
 
   it 'should be able to import some commands from other sets' do
@@ -103,9 +97,7 @@ describe Pry::CommandSet do
     @set.run_command @ctx, 'foo'
     run.should == true
 
-    lambda {
-      @set.run_command @ctx, 'bar'
-    }.should.raise(Pry::NoCommandError)
+    expect { @set.run_command @ctx, 'bar' }.to raise_error Pry::NoCommandError
   end
 
   it 'should return command set after import' do
@@ -211,7 +203,7 @@ describe Pry::CommandSet do
       @set['bar'].options[:interpolate].should == @set['foo'].options[:interpolate]
 
       # however some options should not be inherited
-      @set['bar'].options[:listing].should.not ==  @set['foo'].options[:listing]
+      @set['bar'].options[:listing].should_not ==  @set['foo'].options[:listing]
       @set['bar'].options[:listing].should == "bar"
     end
 
@@ -289,22 +281,19 @@ describe Pry::CommandSet do
   end
 
   it 'should be able to have its own helpers' do
-    @set.command('foo') do
-      should.respond_to :my_helper
-    end
-
-    @set.helpers do
-      def my_helper; end
-    end
+    @set.command('foo') { my_helper }
+    @set.helpers { def my_helper; end }
 
     @set.run_command(@ctx, 'foo')
-    Pry::Command.subclass('foo', '', {}, Module.new).new({:target => binding}).should.not.respond_to :my_helper
+    Pry::Command.subclass('foo', '', {}, Module.new)
+                .new({:target => binding})
+                .should_not(respond_to :my_helper)
   end
 
   it 'should not recreate a new helper module when helpers is called' do
     @set.command('foo') do
-      should.respond_to :my_helper
-      should.respond_to :my_other_helper
+      my_helper
+      my_other_helper
     end
 
     @set.helpers do
@@ -326,7 +315,7 @@ describe Pry::CommandSet do
     end
 
     @set.import imported_set
-    @set.command('foo') { should.respond_to :imported_helper_method }
+    @set.command('foo') { imported_helper_method }
     @set.run_command(@ctx, 'foo')
   end
 
@@ -340,7 +329,7 @@ describe Pry::CommandSet do
     end
 
     @set.import_from imported_set, 'bar'
-    @set.command('foo') { should.respond_to :imported_helper_method }
+    @set.command('foo') { imported_helper_method }
     @set.run_command(@ctx, 'foo')
   end
 
@@ -358,9 +347,7 @@ describe Pry::CommandSet do
     @ctx[:command_set] = @set
     @ctx[:output] = StringIO.new
 
-    lambda {
-      @set.run_command(@ctx, 'help')
-    }.should.not.raise
+    expect { @set.run_command(@ctx, 'help') }.to_not raise_error
   end
 
 
@@ -382,13 +369,13 @@ describe Pry::CommandSet do
     end
 
     it 'should raise exception trying to rename non-existent command' do
-      lambda { @set.rename_command('bar', 'foo') }.should.raise ArgumentError
+      expect { @set.rename_command('bar', 'foo') }.to raise_error ArgumentError
     end
 
     it 'should make old command name inaccessible' do
       @set.command('foo') { }
       @set.rename_command('bar', 'foo')
-      lambda { @set.run_command(@ctx, 'foo') }.should.raise Pry::NoCommandError
+      expect { @set.run_command(@ctx, 'foo') }.to raise_error Pry::NoCommandError
     end
 
     it 'should be able to pass in options when renaming command' do
@@ -592,9 +579,7 @@ describe Pry::CommandSet do
 
     it 'should not cause argument interpolation' do
       cmd = @set.command('hello')
-      lambda {
-        @set.valid_command?('hello #{raise "futz"}')
-      }.should.not.raise
+      expect { @set.valid_command?('hello #{raise "futz"}') }.to_not raise_error
     end
   end