1 files changed, 58 insertions, 0 deletions
diff --git a/test/prism/format_errors_test.rb b/test/prism/format_errors_test.rb
new file mode 100644
index 0000000000..63206d5765
--- /dev/null
+++ b/test/prism/format_errors_test.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require_relative "test_helper"
+
+return if Prism::BACKEND == :FFI
+
+module Prism
+  class FormatErrorsTest < TestCase
+    def test_basic
+      expected = <<~ERROR
+        > 1 | <>
+            | ^ unexpected '<', ignoring it
+            |  ^ unexpected '>', ignoring it
+      ERROR
+
+      assert_equal expected, Debug.format_errors("<>", false)
+    end
+
+    def test_multiple
+      expected = <<~ERROR
+        > 1 | "%W"\\u"
+            |     ^ unexpected backslash, ignoring it
+            |      ^ unexpected local variable or method, expecting end-of-input
+            |        ^ unterminated string meets end of file
+      ERROR
+
+      assert_equal expected, Debug.format_errors('"%W"\u"', false)
+    end
+
+    def test_truncate_start
+      expected = <<~ERROR
+        > 1 | ... <>
+            |     ^ unexpected '<', ignoring it
+            |      ^ unexpected '>', ignoring it
+      ERROR
+
+      assert_equal expected, Debug.format_errors("#{" " * 30}<>", false)
+    end
+
+    def test_truncate_end
+      expected = <<~ERROR
+        > 1 | <#{" " * 30} ...
+            | ^ unexpected '<', ignoring it
+      ERROR
+
+      assert_equal expected, Debug.format_errors("<#{" " * 30}a", false)
+    end
+
+    def test_truncate_both
+      expected = <<~ERROR
+        > 1 | ... <#{" " * 30} ...
+            |     ^ unexpected '<', ignoring it
+      ERROR
+
+      assert_equal expected, Debug.format_errors("#{" " * 30}<#{" " * 30}a", false)
+    end
+  end
+end