Add Go test for tab-indented sibling navigation

Tests the visual column fix by using Go files (which use tabs
by convention). Validates that move_down/move_up correctly
navigate between sibling nodes at the same indentation level
when the file uses tab characters.

Test cases:
- var declarations as siblings
- if blocks as siblings
- top-level function declarations

Author: ahdzib-maya

tests/fixtures/go.go

@@ -0,0 +1,22 @@
+package main
+
+import "fmt"
+
+func main() {
+	var x = 1
+	var y = 2
+	var z = 3
+
+	if x > 0 {
+		fmt.Println("positive")
+	}
+
+	if y > 0 {
+		fmt.Println("also positive")
+	}
+}
+
+func helper() {
+	var a = 10
+	var b = 20
+}

tests/treewalker/go_spec.lua

@@ -0,0 +1,50 @@
+local load_fixture = require "tests.load_fixture"
+local tw = require 'treewalker'
+local h = require 'tests.treewalker.helpers'
+
+describe("Movement in Go file with tab indentation:", function()
+  before_each(function()
+    load_fixture("/go.go")
+    vim.opt.tabstop = 4  -- Standard Go tab width
+  end)
+
+  h.ensure_has_parser("go")
+
+  -- This test validates the visual column fix in targets.lua
+  -- Go files use tabs for indentation, which previously caused
+  -- sibling navigation to fail due to byte vs visual column mismatch
+  it("moves down between tab-indented var declarations (sibling nodes)", function()
+    vim.fn.cursor(6, 1)  -- First var declaration: var x = 1
+    tw.move_down()
+    -- Should move to next sibling var, not skip or go elsewhere
+    local row = vim.fn.line('.')
+    assert.equals(7, row, "Should move from var x to var y (line 7)")
+    tw.move_down()
+    row = vim.fn.line('.')
+    assert.equals(8, row, "Should move from var y to var z (line 8)")
+  end)
+
+  it("moves up between tab-indented var declarations (sibling nodes)", function()
+    vim.fn.cursor(8, 1)  -- Third var declaration: var z = 3
+    tw.move_up()
+    local row = vim.fn.line('.')
+    assert.equals(7, row, "Should move from var z to var y (line 7)")
+    tw.move_up()
+    row = vim.fn.line('.')
+    assert.equals(6, row, "Should move from var y to var x (line 6)")
+  end)
+
+  it("moves down between tab-indented if blocks (sibling nodes)", function()
+    vim.fn.cursor(10, 1)  -- First if block
+    tw.move_down()
+    local row = vim.fn.line('.')
+    assert.equals(14, row, "Should move from first if to second if (line 14)")
+  end)
+
+  it("moves between top-level function declarations", function()
+    vim.fn.cursor(5, 1)  -- func main()
+    tw.move_down()
+    local row = vim.fn.line('.')
+    assert.equals(19, row, "Should move from main to helper (line 19)")
+  end)
+end)