feat(signals): add test-coverage classification to test-evidence

src/signals/test-evidence.ts

@@ -8,6 +8,23 @@
   );
 }
 
 export function hasLocalTestEvidence(input: { tests?: string[] | undefined; testFiles?: string[] | undefined }): boolean {
   return (input.tests ?? []).length > 0 || (input.testFiles ?? []).some((file) => isTestPath(file));
 }
+
+/**
+ * Coarse classification of how much test coverage accompanies a set of changed paths.
+ * Used by slop signals to weight diffs that touch source but include no tests differently
+ * from those with proportionally strong test changes.
+ */
+export type TestCoverageClassification = "strong" | "adequate" | "weak" | "absent";
+
+export function classifyTestCoverage(changedPaths: string[]): TestCoverageClassification {
+  if (changedPaths.length === 0) return "absent";
+  const testCount = changedPaths.filter(isTestPath).length;
+  if (testCount === 0) return "absent";
+  const ratio = testCount / changedPaths.length;
+  if (ratio >= 0.4) return "strong";
+  if (ratio >= 0.2) return "adequate";
+  return "weak";
+}

test/unit/test-evidence.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { hasLocalTestEvidence, isTestPath } from "../../src/signals/test-evidence";
+import { classifyTestCoverage, hasLocalTestEvidence, isTestPath } from "../../src/signals/test-evidence";
 
 describe("test evidence helpers", () => {
   it("detects common test path conventions", () => {
@@ -17,3 +17,29 @@
     expect(hasLocalTestEvidence({})).toBe(false);
   });
 });
+
+describe("classifyTestCoverage", () => {
+  it("classifies an empty path list as absent", () => {
+    expect(classifyTestCoverage([])).toBe("absent");
+  });
+
+  it("classifies a list with no test files as absent", () => {
+    expect(classifyTestCoverage(["src/auth.ts", "src/utils.ts"])).toBe("absent");
+  });
+
+  it("classifies >= 40% test ratio as strong", () => {
+    // 2 source + 2 test = 50%
+    expect(classifyTestCoverage(["src/a.ts", "src/b.ts", "test/a.test.ts", "test/b.test.ts"])).toBe("strong");
+  });
+
+  it("classifies 20%–39% test ratio as adequate", () => {
+    // 3 source + 1 test = 25%
+    expect(classifyTestCoverage(["src/a.ts", "src/b.ts", "src/c.ts", "test/a.test.ts"])).toBe("adequate");
+  });
+
+  it("classifies > 0% but < 20% test ratio as weak", () => {
+    // 9 source + 1 test ≈ 10%
+    const sources = Array.from({ length: 9 }, (_, i) => `src/file${i}.ts`);
+    expect(classifyTestCoverage([...sources, "test/single.test.ts"])).toBe("weak");
+  });
+});