1 files changed, 40 insertions, 0 deletions
diff --git a/tests/pattern/composition.test.py b/tests/pattern/composition.test.py
new file mode 100644
index 0000000..9cf0003
--- /dev/null
+++ b/tests/pattern/composition.test.py
@@ -0,0 +1,40 @@
+"""Tests for the :class:`Pattern` composition surface."""
+
+import pytest
+
+from edify import Pattern, RegexBuilder
+from edify.errors.input import MustBeInstanceError
+
+
+def test_pattern_builds_the_same_element_tree_as_a_builder():
+    pattern = Pattern().between(3, 20).word()
+    builder = RegexBuilder().between(3, 20).word()
+    assert pattern._state == builder._state
+
+
+def test_pattern_has_no_to_regex_terminal():
+    pattern = Pattern().digit()
+    assert not hasattr(pattern, "to_regex")
+
+
+def test_pattern_has_no_to_regex_string_terminal():
+    pattern = Pattern().digit()
+    assert not hasattr(pattern, "to_regex_string")
+
+
+def test_pattern_supports_nested_use_composition():
+    inner = Pattern().one_or_more().digit()
+    outer = Pattern().string("v").use(inner)
+    embedded = RegexBuilder().use(outer)
+    assert embedded.to_regex_string() == "v\\d+"
+
+
+def test_subexpression_still_accepts_a_pattern():
+    pattern = Pattern().at_least(3).word()
+    embedded = RegexBuilder().subexpression(pattern)
+    assert embedded.to_regex_string() == "\\w{3,}"
+
+
+def test_subexpression_rejects_non_builder_input():
+    with pytest.raises(MustBeInstanceError):
+        RegexBuilder().subexpression("not a pattern")