6 files changed, 135 insertions, 10 deletions
diff --git a/tests/indent/c_spec.lua b/tests/indent/c_spec.lua
index 1089ee4eb..f93d7ee22 100644
--- a/tests/indent/c_spec.lua
+++ b/tests/indent/c_spec.lua
@@ -1,5 +1,5 @@
-local whole_file = require('nvim-treesitter.test_utils').indent_whole_file
-local new_line = require('nvim-treesitter.test_utils').indent_new_line
+local whole_file = require('tests.indent.common').indent_whole_file
+local new_line = require('tests.indent.common').indent_new_line
 local scan_dir = require('plenary.scandir').scan_dir
 
 local opts = {
diff --git a/tests/indent/common.lua b/tests/indent/common.lua
new file mode 100644
index 000000000..96caf17f9
--- /dev/null
+++ b/tests/indent/common.lua
@@ -0,0 +1,125 @@
+local M = {}
+
+local assert = require('luassert')
+local say = require('say')
+
+local function same_indent(state, arguments)
+  local before = arguments[1]
+  local after = arguments[2]
+
+  local ok = true
+  local errors = { before = {}, after = {} }
+  for line = 1,#before do
+    if before[line] ~= after[line] then
+      -- store the actual indentation length for each line
+      errors.before[line] = #string.match(before[line], '^%s*')
+      errors.after[line] = #string.match(after[line], '^%s*')
+      ok = false
+    end
+  end
+
+  -- we will always use only a single argument, passing the other one in fmtargs
+  arguments.fmtargs = { { errors = errors, other = after } }
+  arguments.fmtargs[2] = { errors = errors, other = after }
+
+  return ok
+end
+
+local function format_indent(arg, fmtargs)
+  -- find minimal width if any line is longer
+  local width = 40
+  for _, line in ipairs(fmtargs.other) do
+    width = #line > width and #line or width
+  end
+
+  width = width + 3
+  local header_fmt = '%8s %2s%-' .. tostring(width + 1) .. 's %s'
+  local fmt = '%8s %2s |%-' .. tostring(width) .. 's |%s'
+
+  local output = {header_fmt:format('', '', 'Found:', 'Expected:')}
+
+  for i, line in ipairs(arg) do
+    if fmtargs.errors.before[i] then
+      local indents = string.format('%d vs %d', fmtargs.errors.after[i], fmtargs.errors.before[i])
+      table.insert(output, fmt:format(indents, '=>', fmtargs.other[i], line))
+    else
+      table.insert(output, fmt:format('', '', fmtargs.other[i], line))
+    end
+  end
+
+  return table.concat(output, '\n')
+end
+
+say:set_namespace('en')
+say:set('assertion.same_indent.positive', 'Incorrect indentation\n%s')
+say:set('assertion.same_indent.negative', 'Incorrect indentation\n%s')
+assert:register('assertion', 'same_indent', same_indent,
+  'assertion.same_indent.positive', 'assert.same_indent.negative')
+
+-- Custom assertion better suited for indentation diffs
+local function compare_indent(before, after)
+  assert:add_formatter(format_indent)
+  assert.is.same_indent(before, after)
+  assert:remove_formatter(format_indent)
+end
+
+local function set_buf_indent_opts(opts)
+  local optnames = {'tabstop', 'shiftwidth', 'softtabstop', 'expandtab', 'filetype'}
+  for _, opt in ipairs(optnames) do
+    if opts[opt] ~= nil then
+      vim.bo[opt] = opts[opt]
+    end
+  end
+end
+
+function M.run_indent_test(file, runner, opts)
+  assert.are.same(1, vim.fn.filereadable(file))
+
+  -- load reference file
+  vim.cmd(string.format('edit %s', file))
+  local before = vim.api.nvim_buf_get_lines(0, 0, -1, true)
+
+  assert.are.same('nvim_treesitter#indent()', vim.bo.indentexpr)
+  set_buf_indent_opts(opts)
+
+  -- perform the test
+  runner()
+
+  -- get file content after the test