chore: Add property tests for formatters

.gitignore

@@ -4,6 +4,7 @@
 *.swp
 __pycache__
 .pyc
+.hypothesis
 
 # sample repo
 tests/fixtures/sample-workspace

bough/formatters.py

@@ -113,7 +113,7 @@ def dependency_graph(analyzer: BoughAnalyzer) -> str:
         lines.extend(_render_graph(buildable, "🚀 Buildable Packages:", warning=True))
 
     if libraries:
-        lines.extend(_render_graph(buildable, "📚 Library Packages:"))
+        lines.extend(_render_graph(libraries, "📚 Library Packages:"))
 
     if not buildable and not libraries:
         lines.append("No packages found in workspace.")

pyproject.toml

@@ -25,6 +25,7 @@ source = "vcs"
 
 [dependency-groups]
 dev = [
+    "hypothesis>=6.143.1",
     "ipdb>=0.13.13",
     "pytest>=8.4.1",
     "pytest-cov>=7.0.0",

tests/test_formatters.py

@@ -0,0 +1,109 @@
+from hypothesis import given, strategies as st
+from unittest.mock import Mock
+from pathlib import Path
+import json
+import bough.formatters as sut
+
+package_name = st.text(
+    min_size=1, 
+    max_size=20,
+    alphabet=st.characters(blacklist_characters='\n\r')
+)
+
+packages = st.sets(package_name, min_size=1)
+files = st.sets(package_name, min_size=1)
+
+@given(packages)
+def test_github_matrix_always_valid_json(package_names):
+    """GitHub matrix output must always be valid JSON."""
+    analyzer = Mock()
+    analyzer.packages = {
+        name: Mock(directory=Path(f"/root/{name}"))
+        for name in package_names
+    }
+    analyzer.workspace_root = Path("/root")
+
+    result = sut.github_matrix(analyzer, package_names)
+    parsed = json.loads(result)
+
+    assert len(parsed["include"]) == len(package_names)
+    assert all("package" in item for item in parsed["include"])
+
+
+@given(packages)
+def test_quiet_output_has_correct_line_count(package_names):
+    """Quiet mode outputs exactly one line per package."""
+    analyzer = Mock()
+    analyzer.packages = {
+        name: Mock(directory=Path(f"/root/{name}"))
+        for name in package_names
+    }
+
+    result = sut.quiet(analyzer, package_names)
+
+    assert len(result.split("\n")) == len(package_names)
+
+
+@given(packages, files)
+def test_human_readable_contains_all_packages(packages, files):
+    """All package names must appear in human readable output."""
+    analyzer = Mock()
+    analyzer.packages = {
+        name: Mock(directory=Path(f"/root/{name}"))
+        for name in packages
+    }
+    analyzer.workspace_root = Path("/root")
+
+    result = sut.human_readable(analyzer, packages, files)
+
+    for pkg in packages:
+        assert pkg in result
+
+
+
+@st.composite
+def package_graph(draw):
+    """Generate a set of packages with dependencies referencing each other."""
+    num_packages = draw(st.integers(min_value=1, max_value=10))
+    names = [draw(package_name) for _ in range(num_packages)]
+    names = list(set(names))
+
+    packages = []
+    for name in names:
+        deps = draw(st.sets(st.sampled_from(names), max_size=3)) - {name}
+        is_buildable = draw(st.booleans())
+        packages.append({
+            "name": name,
+            "dependencies": deps,
+            "is_buildable": is_buildable
+        })
+
+    return packages
+
+@given(package_graph())
+def test_dependency_graph_contains_all_packages(packages):
+    """All package names must appear in dependency graph output."""
+    analyzer = Mock()
+    analyzer.packages = {
+        pkg["name"]: Mock(
+            directory=Path(f"/root/{pkg['name']}"),
+            dependencies=pkg["dependencies"]
+        )
+        for pkg in packages
+    }
+    analyzer.workspace_root = Path("/root")
+
+    # Build reverse dependency graph
+    analyzer.dependency_graph = {name: set() for name in analyzer.packages}
+    for pkg in packages:
+        for dep in pkg["dependencies"]:
+            if dep in analyzer.dependency_graph:
+                analyzer.dependency_graph[dep].add(pkg["name"])
+
+    buildable_names = {pkg["name"] for pkg in packages if pkg["is_buildable"]}
+    analyzer._is_buildable_package = lambda p: p.directory.name in buildable_names
+
+    result = sut.dependency_graph(analyzer)
+
+    for pkg in packages:
+        assert pkg["name"] in result