fix: a few edge cases with zero entities

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Hits count for test coverage. [#91]
 
+### Fixed
+- Few edge cases with zero entities. [#92]
+
 ## [0.3.10] - 2025-10-12
 ### Added
 - Support for `dbt==1.9`. [#85]

dbt_coverage/__init__.py

@@ -323,16 +323,12 @@ class ColumnRef:
     covered: Set[ColumnRef]
     total: Set[ColumnRef]
     misses: Set[ColumnRef] = field(init=False)
-    coverage: float = field(init=False)
+    coverage: Optional[float] = field(init=False)
     subentities: Dict[str, CoverageReport]
 
     def __post_init__(self):
-        if self.covered is not None and self.total is not None and len(self.total) != 0:
-            self.misses = self.total - self.covered
-            self.coverage = len(self.covered) / len(self.total)
-        else:
-            self.misses = None
-            self.coverage = None
+        self.misses = self.total - self.covered
+        self.coverage = len(self.covered) / len(self.total) if self.total else None
 
     @classmethod
     def from_catalog(cls, catalog: Catalog, cov_type: CoverageType):
@@ -584,9 +580,12 @@ def summary(self):
 
         buf.write(f"{'':10}{'before':>10}{'after':>10}{'+/-':>15}\n")
         buf.write("=" * 45 + "\n")
+
+        before_cov = self.before.coverage if self.before.coverage is not None else 0.0
+        after_cov = self.after.coverage if self.after.coverage is not None else 0.0
         buf.write(
-            f"{'Coverage':10}{self.before.coverage:10.2%}{self.after.coverage:10.2%}"
-            f"{(self.after.coverage - self.before.coverage):+15.2%}\n"
+            f"{'Coverage':10}{before_cov:10.2%}{after_cov:10.2%}"
+            f"{(after_cov - before_cov):+15.2%}\n"
         )
         buf.write("=" * 45 + "\n")
 
@@ -684,10 +683,16 @@ def _new_miss_summary_row(self):
 
         before_covered = len(self.before.covered) if self.before is not None else "-"
         before_total = len(self.before.total) if self.before is not None else "-"
-        before_coverage = f"({self.before.coverage:.2%})" if self.before is not None else "(-)"
+        before_coverage = (
+            f"({self.before.coverage:.2%})"
+            if self.before is not None and self.before.coverage is not None
+            else "(-)"
+        )
         after_covered = len(self.after.covered)
         after_total = len(self.after.total)
-        after_coverage = f"({self.after.coverage:.2%})"
+        after_coverage = (
+            f"({self.after.coverage:.2%})" if self.after.coverage is not None else "(-)"
+        )
 
         buf = io.StringIO()
         buf.write(f"{title:50}")

tests/unit/test_init.py

@@ -1,6 +1,6 @@
 import pytest
 
-from dbt_coverage import Catalog, CoverageReport, CoverageType
+from dbt_coverage import Catalog, CoverageDiff, CoverageReport, CoverageType
 
 
 @pytest.mark.parametrize("cov_type", [CoverageType.DOC, CoverageType.TEST])
@@ -15,5 +15,16 @@ def test_coverage_report_with_zero_tables(cov_type):
     assert coverage_report.hits == 0
     assert len(coverage_report.total) == 0
     assert coverage_report.coverage is None
-    assert coverage_report.misses is None
+    assert len(coverage_report.misses) == 0
     assert coverage_report.subentities == {}
+
+
+@pytest.mark.parametrize("cov_type", [CoverageType.DOC, CoverageType.TEST])
+def test_coverage_diff_with_zero_tables(cov_type):
+    empty_catalog = Catalog(tables={})
+    coverage_report_1 = CoverageReport.from_catalog(empty_catalog, cov_type)
+    coverage_report_2 = CoverageReport.from_catalog(empty_catalog, cov_type)
+
+    diff = CoverageDiff(coverage_report_1, coverage_report_2)
+
+    assert len(diff.new_misses) == 0