1 files changed, 92 insertions, 0 deletions
diff --git a/tests/introspect/visualize.test.py b/tests/introspect/visualize.test.py
new file mode 100644
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+++ b/tests/introspect/visualize.test.py
@@ -0,0 +1,92 @@
+"""Tests for the visualize dispatcher in :mod:`edify.introspect.visualize`."""
+
+import pytest
+
+from edify import RegexBuilder
+from edify.elements.types.leaves import DigitElement
+from edify.errors.introspect import (
+    UnsupportedVisualizationEngineError,
+    UnsupportedVisualizationFormatError,
+)
+from edify.introspect.visualize import visualize_elements
+
+
+def _digit_regex():
+    return RegexBuilder().digit().to_regex()
+
+
+def test_default_format_and_engine_produce_ascii_railroad_output():
+    output = visualize_elements((DigitElement(),))
+    assert "| START |" in output
+    assert "| digit |" in output
+    assert "| END |" in output
+
+
+def test_explicit_ascii_format_and_engine_produce_ascii_railroad_output():
+    output = visualize_elements((DigitElement(),), format="ascii", engine="ascii")
+    assert "| digit |" in output
+
+
+def test_ascii_format_with_wrong_engine_raises_engine_error():
+    with pytest.raises(UnsupportedVisualizationEngineError):
+        visualize_elements((DigitElement(),), format="ascii", engine="graphviz")
+
+
+def test_svg_format_with_graphviz_engine_produces_svg_output():
+    regex = _digit_regex()
+    output = visualize_elements(regex.elements, format="svg", engine="graphviz")
+    assert "</svg>" in output
+
+
+def test_svg_format_with_wrong_engine_raises_engine_error():
+    with pytest.raises(UnsupportedVisualizationEngineError):
+        visualize_elements((DigitElement(),), format="svg", engine="ascii")
+
+
+def test_unknown_format_raises_format_error():
+    with pytest.raises(UnsupportedVisualizationFormatError):
+        visualize_elements((DigitElement(),), format="pdf")
+
+
+def test_unknown_format_error_names_the_received_format_in_message():
+    with pytest.raises(UnsupportedVisualizationFormatError) as excinfo:
+        visualize_elements((DigitElement(),), format="mermaid")
+    assert "'mermaid'" in str(excinfo.value)
+
+
+def test_engine_error_names_both_format_and_engine_in_message():
+    with pytest.raises(UnsupportedVisualizationEngineError) as excinfo:
+        visualize_elements((DigitElement(),), format="ascii", engine="mermaid")
+    message = str(excinfo.value)
+    assert "'ascii'" in message
+    assert "'mermaid'" in message
+
+
+def test_regex_visualize_end_to_end_defaults_to_ascii():
+    regex = _digit_regex()
+    output = regex.visualize()
+    assert "| digit |" in output
+
+
+def test_regex_visualize_svg_end_to_end():
+    regex = _digit_regex()
+    output = regex.visualize(format="svg", engine="graphviz")
+    assert "</svg>" in output
+
+
+def test_regex_visualize_rejects_unknown_format_end_to_end():
+    regex = _digit_regex()
+    with pytest.raises(UnsupportedVisualizationFormatError):
+        regex.visualize(format="dot")
+
+
+def test_regex_visualize_rejects_engine_mismatch_end_to_end():
+    regex = _digit_regex()
+    with pytest.raises(UnsupportedVisualizationEngineError):
+        regex.visualize(format="svg", engine="ascii")
+
+
+def test_empty_elements_still_render_start_and_end():
+    output = visualize_elements(())
+    assert "START" in output
+    assert "END" in output