diff --git a/tests/data/sites/draft_content/config.yml b/tests/data/sites/draft_content/config.yml
new file mode 100644
index 0000000..4052e1d
--- /dev/null
+++ b/tests/data/sites/draft_content/config.yml
@@ -0,0 +1,2 @@
+name: Draft Content Test
+template: plain
diff --git a/tests/data/sites/draft_content/content/draft.md b/tests/data/sites/draft_content/content/draft.md
new file mode 100644
index 0000000..c4bc098
--- /dev/null
+++ b/tests/data/sites/draft_content/content/draft.md
@@ -0,0 +1,9 @@
+---
+type: article
+section: posts
+slug: draft-post
+title: Draft
+date: 2026-08-28
+draft: true
+---
+Draft.
diff --git a/tests/data/sites/draft_content/content/published.md b/tests/data/sites/draft_content/content/published.md
new file mode 100644
index 0000000..d670809
--- /dev/null
+++ b/tests/data/sites/draft_content/content/published.md
@@ -0,0 +1,8 @@
+---
+type: article
+section: posts
+slug: published
+title: Published
+date: 2026-08-28
+---
+Published.
diff --git a/tests/data/sites/duplicate_slug/config.yml b/tests/data/sites/duplicate_slug/config.yml
new file mode 100644
index 0000000..281dd28
--- /dev/null
+++ b/tests/data/sites/duplicate_slug/config.yml
@@ -0,0 +1,2 @@
+name: Duplicate Slug Test
+template: plain
diff --git a/tests/data/sites/duplicate_slug/content/first.md b/tests/data/sites/duplicate_slug/content/first.md
new file mode 100644
index 0000000..69a3a78
--- /dev/null
+++ b/tests/data/sites/duplicate_slug/content/first.md
@@ -0,0 +1,8 @@
+---
+type: article
+section: posts
+slug: hello
+title: First
+date: 2026-08-28
+---
+First.
diff --git a/tests/data/sites/duplicate_slug/content/second.md b/tests/data/sites/duplicate_slug/content/second.md
new file mode 100644
index 0000000..9c40e6c
--- /dev/null
+++ b/tests/data/sites/duplicate_slug/content/second.md
@@ -0,0 +1,8 @@
+---
+type: article
+section: posts
+slug: hello
+title: Second
+date: 2026-08-28
+---
+Second.
diff --git a/tests/unit/conftest.py b/tests/unit/conftest.py
index 79c04cd..33a7418 100644
--- a/tests/unit/conftest.py
+++ b/tests/unit/conftest.py
@@ -7,14 +7,22 @@ DATA_SITES = Path(__file__).parent.parent / "data" / "sites"
 
 
 @pytest.fixture
-def make_site(tmp_path):
-    def _make(name, **kwargs):
-        site_dir = tmp_path / name
+def site_dir(tmp_path):
+    def _make(name):
+        path = tmp_path / name
         shutil.copytree(
             DATA_SITES / name,
-            site_dir,
+            path,
             ignore=shutil.ignore_patterns("output", "build.log"),
         )
-        return Site(site_dir, **kwargs)
+        return path
+
+    return _make
+
+
+@pytest.fixture
+def make_site(site_dir):
+    def _make(name, **kwargs):
+        return Site(site_dir(name), **kwargs)
 
     return _make
diff --git a/tests/unit/test_site.py b/tests/unit/test_site.py
index 431ed96..bfcd305 100644
--- a/tests/unit/test_site.py
+++ b/tests/unit/test_site.py
@@ -1,6 +1,7 @@
 from pathlib import Path
 import pytest
-from omicron.ssg.site import Site
+from omicron.ssg.output import ContentError, Directory
+from omicron.ssg.site import ConfigError, Site
 
 
 @pytest.mark.parametrize(
@@ -17,3 +18,83 @@ def test_parse_base_url(value, expected_origin, expected_path):
     origin, path = Site.parse_base_url(value)
     assert origin == expected_origin
     assert path == expected_path
+
+
+def test_discover_raises_on_duplicate_destination(make_site):
+    site = make_site("duplicate_slug")
+    with pytest.raises(ContentError):
+        site.discover()
+
+
+def test_discover_creates_content_directories(make_site):
+    site = make_site("main")
+    site.discover()
+
+    assert isinstance(site.by_path[Path("posts")], Directory)
+    assert isinstance(site.by_path[Path("posts/first-post")], Directory)
+
+
+def test_read_config_errors(site_dir):
+    path = site_dir("thin_site")
+    config_path = path / "config.yml"
+
+    config_path.unlink()
+    with pytest.raises(ConfigError, match="config file missing"):
+        Site(path)
+
+    config_path.write_text("- a\n- b\n")
+    with pytest.raises(ConfigError, match="YAML mapping with string keys"):
+        Site(path)
+
+    config_path.write_text("123: value\n")
+    with pytest.raises(ConfigError, match="YAML mapping with string keys"):
+        Site(path)
+
+    config_path.write_text("template: plain\n")
+    with pytest.raises(ConfigError, match="name value missing"):
+        Site(path)
+
+    config_path.write_text("name: test\n")
+    with pytest.raises(ConfigError, match="template value missing"):
+        Site(path)
+
+
+def test_build_raises_for_relative_base_url(site_dir):
+    path = site_dir("thin_site")
+    (path / "config.yml").write_text("name: test\ntemplate: plain\nbase_url: blog\n")
+
+    site = Site(path)
+    with pytest.raises(ConfigError, match="absolute path"):
+        site.build()
+
+
+def test_discover_skips_drafts_by_default(make_site):
+    site = make_site("draft_content")
+    site.discover()
+
+    assert len(site.content) == 1
+    assert site.content[0].title == "Published"
+
+
+def test_discover_includes_drafts_when_enabled(make_site):
+    site = make_site("draft_content", drafts=True)
+    site.discover()
+
+    assert len(site.content) == 2
+
+
+def test_clean_removes_output_directory(make_site):
+    site = make_site("main")
+    site.build()
+    assert site.output_path.exists()
+
+    site.clean()
+    assert not site.output_path.exists()
+
+    site.clean()
+    assert not site.output_path.exists()
+
+
+def test_resolve_template_path_raises_for_missing_template():
+    with pytest.raises(ConfigError, match="not found"):
+        Site.resolve_template_path("does-not-exist")