Lua: add methods insert, remove, and sort to pandoc.List

The functions `table.insert`, `table.remove`, and `table.sort` are added
to pandoc.List elements.  They can be used as methods, e.g.

    local numbers = pandoc.List {2, 3, 1}
    numbers:sort()     -- numbers is now {1, 2, 3}

test/lua/module/pandoc-list.lua

@@ -15,33 +15,6 @@ return {
     end)
   },
 
-  group 'new' {
-    test('make table usable as list', function ()
-      local test = List:new{1, 1, 2, 3, 5}
-      assert.are_same(
-        {1, 1, 4, 9, 25},
-        test:map(function (x) return x^2 end)
-      )
-    end),
-    test('return empty list if no argument is given', function ()
-       assert.are_same({}, List:new())
-    end),
-    test('metatable of result is pandoc.List', function ()
-      local test = List:new{5}
-      assert.are_equal(List, getmetatable(test))
-    end)
-  },
-
-  group 'includes' {
-    test('finds elements in list', function ()
-      local lst = List:new {'one', 'two', 'three'}
-      assert.is_truthy(lst:includes('one'))
-      assert.is_truthy(lst:includes('two'))
-      assert.is_truthy(lst:includes('three'))
-      assert.is_falsy(lst:includes('four'))
-    end)
-  },
-
   group 'clone' {
     test('changing the clone does not affect original', function ()
       local orig = List:new {23, 42}
@@ -54,7 +27,25 @@ return {
       local orig = List:new {23, 42}
       assert.are_equal(List, getmetatable(orig:clone()))
     end),
-                },
+  },
+
+  group 'extend' {
+    test('extends list with other list', function ()
+      local primes = List:new {2, 3, 5, 7}
+      primes:extend {11, 13, 17}
+      assert.are_same({2, 3, 5, 7, 11, 13, 17}, primes)
+    end)
+  },
+
+  group 'filter' {
+    test('keep elements for which property is truthy', function ()
+      local is_small_prime = function (x)
+        return List.includes({2, 3, 5, 7}, x)
+      end
+      local numbers = List:new {4, 7, 2, 9, 5, 11}
+      assert.are_same({7, 2, 5}, numbers:filter(is_small_prime))
+    end),
+  },
 
   group 'find' {
     test('returns element and index if found', function ()
@@ -87,11 +78,26 @@ return {
     end),
   },
 
-  group 'extend' {
-    test('extends list with other list', function ()
-      local primes = List:new {2, 3, 5, 7}
-      primes:extend {11, 13, 17}
-      assert.are_same({2, 3, 5, 7, 11, 13, 17}, primes)
+  group 'includes' {
+    test('finds elements in list', function ()
+      local lst = List:new {'one', 'two', 'three'}
+      assert.is_truthy(lst:includes('one'))
+      assert.is_truthy(lst:includes('two'))
+      assert.is_truthy(lst:includes('three'))
+      assert.is_falsy(lst:includes('four'))
+    end)
+  },
+
+  group 'insert' {
+    test('insert value at end of list.', function ()
+      local count_norsk = List {'en', 'to', 'tre'}
+      count_norsk:insert('fire')
+      assert.are_same({'en', 'to', 'tre', 'fire'}, count_norsk)
+    end),
+    test('insert value in the middle of list.', function ()
+      local count_norsk = List {'fem', 'syv'}
+      count_norsk:insert(2, 'seks')
+      assert.are_same({'fem', 'seks', 'syv'}, count_norsk)
     end)
   },
 
@@ -108,13 +114,47 @@ return {
     end)
   },
 
-  group 'filter' {
-    test('keep elements for which property is truthy', function ()
-      local is_small_prime = function (x)
-        return List.includes({2, 3, 5, 7}, x)
-      end
-      local numbers = List:new {4, 7, 2, 9, 5, 11}
-      assert.are_same({7, 2, 5}, numbers:filter(is_small_prime))
+  group 'new' {
+    test('make table usable as list', function ()
+      local test = List:new{1, 1, 2, 3, 5}
+      assert.are_same(
+        {1, 1, 4, 9, 25},
+        test:map(function (x) return x^2 end)
+      )
     end),
+    test('return empty list if no argument is given', function ()
+       assert.are_same({}, List:new())
+    end),
+    test('metatable of result is pandoc.List', function ()
+      local test = List:new{5}
+      assert.are_equal(List, getmetatable(test))
+    end)
+  },
+
+  group 'remove' {
+    test('remove value at end of list.', function ()
+      local understand = List {'jeg', 'forstår', 'ikke'}
+      local norsk_not = understand:remove()
+      assert.are_same({'jeg', 'forstår'}, understand)
+      assert.are_equal('ikke', norsk_not)
+    end),
+    test('remove value at beginning of list.', function ()
+      local count_norsk = List {'en', 'to', 'tre'}
+      count_norsk:remove(1)
+      assert.are_same({'to', 'tre'}, count_norsk)
+    end)
+  },
+
+  group 'sort' {
+    test('sort numeric list', function ()
+      local numbers = List {71, 5, -1, 42, 23, 0, 1}
+      numbers:sort()
+      assert.are_same({-1, 0, 1, 5, 23, 42, 71}, numbers)
+    end),
+    test('reverse-sort numeric', function ()
+      local numbers = List {71, 5, -1, 42, 23, 0, 1}
+      numbers:sort(function (x, y) return x > y end)
+      assert.are_same({71, 42, 23, 5, 1, 0, -1}, numbers)
+    end)
   },
 }