Add method body -> super mutation

- Mutates method bodies to `super` to catch cases where a method has
  been needlessly re-implemented and the parent class provides the
  equivalent behavior.
- Closes mbj#154
- Closes mbj#673

lib/mutant/mutator/node/define.rb

@@ -14,6 +14,7 @@ def dispatch
           emit_optarg_body_assignments
           emit_restarg_body_mutation
           emit_body(N_RAISE)
+          emit_body(N_ZSUPER)
           emit_body(nil)
           emit_body_mutations if body
         end

meta/def.rb

@@ -2,6 +2,7 @@
   source 'def foo; end'
 
   mutation 'def foo; raise; end'
+  mutation 'def foo; super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -14,6 +15,7 @@
   mutation 'def foo(a); nil; end'
   mutation 'def foo(*b); nil; end'
   mutation 'def foo(a, *b); b = []; nil; end'
+  mutation 'def foo(a, *b); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -25,6 +27,7 @@
   mutation 'def foo(a, *); raise; end'
   mutation 'def foo(a); nil; end'
   mutation 'def foo(*); nil; end'
+  mutation 'def foo(a, *); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -34,6 +37,7 @@
   mutation 'def foo; nil; rescue; end'
   mutation 'def foo; self; rescue; end'
   mutation 'def foo; end'
+  mutation 'def foo; super; end'
 
   # Promote rescue resbody bodies
   mutation 'def foo; foo; end'
@@ -65,6 +69,8 @@
   # Failing body
   mutation 'def a; raise; end'
 
+  # Superclass implementation
+  mutation 'def a; super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -85,6 +91,7 @@
 
   mutation 'def foo; raise; end'
 
+  mutation 'def foo; super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -103,7 +110,7 @@
 
   # Mutation of body
   mutation 'def foo(a, b); raise; end'
-
+  mutation 'def foo(a, b); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -120,13 +127,15 @@
   mutation 'def foo(b = nil); true; end'
   mutation 'def foo(a, _b = nil); true; end'
   mutation 'def foo(a, b); true; end'
+  mutation 'def foo(a, b = nil); super; end'
 end
 
 Mutant::Meta::Example.add :def do
   source 'def foo(_unused); end'
 
   mutation 'def foo(_unused); raise; end'
   mutation 'def foo; end'
+  mutation 'def foo(_unused); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -137,6 +146,7 @@
   mutation 'def foo(_unused = true); raise; end'
   mutation 'def foo(_unused); end'
   mutation 'def foo; end'
+  mutation 'def foo(_unused = true); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -158,6 +168,7 @@
   mutation 'def foo(a = 0, b = 0); a = 0; end'
   mutation 'def foo(a = 0, b = 0); b = 0; end'
   mutation 'def foo(a = 0, b = 0); raise; end'
+  mutation 'def foo(a = 0, b = 0); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -170,6 +181,7 @@
   mutation 'def foo(_a = true); end'
   mutation 'def foo(a = true); raise; end'
   mutation 'def foo(a = true); a = true; end'
+  mutation 'def foo(a = true); super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -189,6 +201,8 @@
   mutation 'def self.foo; end'
 
   mutation 'def self.foo; raise; end'
+
+  mutation 'def self.foo; super; end'
 end
 
 Mutant::Meta::Example.add :def do
@@ -208,4 +222,5 @@
 
   # Mutation of body
   mutation 'def self.foo(a, b); raise; end'
+  mutation 'def self.foo(a, b); super; end'
 end

meta/kwarg.rb

@@ -3,5 +3,6 @@
 
   mutation 'def foo; end'
   mutation 'def foo(bar:); raise; end'
+  mutation 'def foo(bar:); super; end'
   mutation 'def foo(_bar:); end'
 end

meta/kwoptarg.rb

@@ -3,6 +3,7 @@
 
   mutation 'def foo; end'
   mutation 'def foo(bar: baz); raise; end'
+  mutation 'def foo(bar: baz); super; end'
   mutation 'def foo(bar: nil); end'
   mutation 'def foo(bar: self); end'
   mutation 'def foo(bar:); end'

meta/rescue.rb

@@ -74,6 +74,9 @@
 
   # Failing body
   mutation 'def a; raise; end'
+
+  # Superclass implementation
+  mutation 'def a; super; end'
 end
 
 Mutant::Meta::Example.add :rescue do

meta/restarg.rb

@@ -4,4 +4,5 @@
   mutation 'def foo; end'
   mutation 'def foo(*bar); bar = []; end'
   mutation 'def foo(*bar); raise; end'
+  mutation 'def foo(*bar); super; end'
 end

spec/unit/mutant/subject/method/instance_spec.rb

@@ -116,6 +116,11 @@ def foo; end
           s(:begin,
             s(:def, :foo, s(:args), s(:send, nil, :raise)), s(:send, nil, :memoize, s(:args, s(:sym, :foo))))
         ),
+        Mutant::Mutation::Evil.new(
+          object,
+          s(:begin,
+            s(:def, :foo, s(:args), s(:zsuper)), s(:send, nil, :memoize, s(:args, s(:sym, :foo))))
+        ),
         Mutant::Mutation::Evil.new(
           object,
           s(:begin,