legacy tests: migrate test_insertcount

src/nvim/testdir/test_insertcount.in

@@ -1,14 +0,0 @@
-Tests for repeating insert and replace.
-
-STARTTEST
-:so small.vim
-:/Second
-4gro
-:/^First/,$wq! test.out
-:" get here when failed and in Insert mode
-:.wq! test.out
-ENDTEST
-
-First line
-Second line
-Last line

src/nvim/testdir/test_insertcount.ok

@@ -1,3 +0,0 @@
-First line
-ooooecond line
-Last line

test/functional/legacy/insertcount_spec.lua

@@ -0,0 +1,24 @@
+-- Tests for repeating insert and replace.
+
+local helpers = require('test.functional.helpers')
+local clear, feed, insert = helpers.clear, helpers.feed, helpers.insert
+local execute, expect = helpers.execute, helpers.expect
+
+describe('insertcount', function()
+  setup(clear)
+
+  it('is working', function()
+    insert([[
+      First line
+      Second line
+      Last line]])
+
+    execute('/Second')
+    feed('4gro')
+
+    expect([[
+      First line
+      oooond line
+      Last line]])
+  end)
+end)