test: reorg #15698

Problem:
Subdirectories like "visual", "insert", "normal" encourage people to
separate *related* tests for no good reason.  Typically the _mode_ is
not the relevant topic of a test (and when it is, _then_ create
an appropriate describe() or it()).

Solution:
- Delete the various `test/functional/<mode>/` subdirectories, move
  their tests to more meaningful topics.
- Rename `…/normal/` to `…/editor/`.
  - Move or merge `…/visual/*` and `…/insert/*` tests into here where
    appropriate.
- Rename `…/eval/` to `…/vimscript/`.
  - Move `…/viml/*` into here also.

* test(reorg): insert/* => editor/mode_insert_spec.lua
* test(reorg): cmdline/* => editor/mode_cmdline_spec.lua
* test(reorg): eval core tests => eval_spec.lua

test/functional/vimscript/getline_spec.lua

@@ -0,0 +1,39 @@
+local helpers = require('test.functional.helpers')(after_each)
+
+local call = helpers.call
+local clear = helpers.clear
+local eq = helpers.eq
+local expect = helpers.expect
+
+describe('getline()', function()
+  before_each(function()
+    clear()
+    call('setline', 1, {'a', 'b', 'c'})
+    expect([[
+      a
+      b
+      c]])
+  end)
+
+  it('returns empty string for invalid line', function()
+    eq('', call('getline', -1))
+    eq('', call('getline', 0))
+    eq('', call('getline', 4))
+  end)
+
+  it('returns empty list for invalid range', function()
+    eq({}, call('getline', 2, 1))
+    eq({}, call('getline', -1, 1))
+    eq({}, call('getline', 4, 4))
+  end)
+
+  it('returns value of valid line', function()
+    eq('b', call('getline', 2))
+    eq('a', call('getline', '.'))
+  end)
+
+  it('returns value of valid range', function()
+    eq({'a', 'b'}, call('getline', 1, 2))
+    eq({'a', 'b', 'c'}, call('getline', 1, 4))
+  end)
+end)