test: Add tests for the python provider

These tests were adapted from the python-client repository

test/functional/runtime/autoload/provider/python_spec.lua

@@ -0,0 +1,93 @@
+do
+  local proc =
+    io.popen([[python -c 'import neovim, sys; sys.stdout.write("ok")' 2> /dev/null]])
+  if proc:read() ~= 'ok' then
+    -- Don't run these tests if python is not available
+    return
+  end
+end
+
+
+local helpers = require('test.functional.helpers')
+local eval, command, feed = helpers.eval, helpers.command, helpers.feed
+local eq, clear, insert = helpers.eq, helpers.clear, helpers.insert
+local expect = helpers.expect
+
+
+describe('python commands and functions', function()
+  before_each(function()
+    clear()
+    command('python import vim')
+  end)
+
+  describe('feature test', function()
+    it('ok', function()
+      eq(1, eval('has("python")'))
+    end)
+  end)
+
+  describe('python_execute', function()
+    it('ok', function()
+      command('python vim.vars["set_by_python"] = [100, 0]')
+      eq({100, 0}, eval('g:set_by_python'))
+    end)
+  end)
+
+  describe('python_execute with nested commands', function()
+    it('ok', function()
+      command([[python vim.command('python vim.command("python vim.command(\'let set_by_nested_python = 555\')")')]])
+      eq(555, eval('g:set_by_nested_python'))
+    end)
+  end)
+
+  describe('python_execute with range', function()
+    it('ok', function()
+      insert([[
+        line1
+        line2
+        line3
+        line4]])
+      feed('ggjvj:python vim.vars["range"] = vim.current.range[:]<CR>')
+      eq({'line2', 'line3'}, eval('g:range'))
+    end)
+  end)
+
+  describe('pyfile', function()
+    it('ok', function()
+      local fname = 'pyfile.py'
+      local F = io.open(fname, 'w')
+      F:write('vim.command("let set_by_pyfile = 123")')
+      F:close()
+      command('pyfile pyfile.py')
+      eq(123, eval('g:set_by_pyfile'))
+      os.remove(fname)
+    end)
+  end)
+
+  describe('pydo', function()
+    it('ok', function()
+      -- :pydo 42 returns None for all lines,
+      -- the buffer should not be changed
+      command('normal :pydo 42')
+      eq(0, eval('&mod'))
+      -- insert some text
+      insert('abc\ndef\nghi')
+      expect([[
+        abc
+        def
+        ghi]])
+      -- go to top and select and replace the first two lines
+      feed('ggvj:pydo return str(linenr)<CR>')
+      expect([[
+        1
+        2
+        ghi]])
+    end)
+  end)
+
+  describe('pyeval', function()
+    it('ok', function()
+      eq({1, 2, {['key'] = 'val'}}, eval([[pyeval('[1, 2, {"key": "val"}]')]]))
+    end)
+  end)
+end)