diff --git a/src/signals/test-evidence.ts b/src/signals/test-evidence.ts
index 928dff87a9..227e64fd30 100644
--- a/src/signals/test-evidence.ts
+++ b/src/signals/test-evidence.ts
@@ -3,6 +3,7 @@ export function isTestPath(file: string): boolean {
     /(^|\/)(test|tests|spec|__tests__)\//i.test(file) ||
     /(^|\/)src\/test\//i.test(file) ||
     /(^|\/)[^/]+_test\.(go|py|rb)$/i.test(file) ||
+    /(^|\/)test_[^/]*\.py$/i.test(file) || // pytest's default `test_*.py` prefix convention (the suffix rule above only catches `*_test.py`)
     /(^|\/)[^/]+_spec\.rb$/i.test(file) ||
     /\.(test|spec)\.(ts|tsx|js|jsx|py|rb|rs)$/i.test(file) ||
     /(^|\/)[^/]+\.(cy|e2e)\.(ts|tsx|js|jsx)$/i.test(file) ||
diff --git a/test/unit/test-evidence.test.ts b/test/unit/test-evidence.test.ts
index f0997c4b5b..aaa82aaaf5 100644
--- a/test/unit/test-evidence.test.ts
+++ b/test/unit/test-evidence.test.ts
@@ -17,6 +17,15 @@ describe("test evidence helpers", () => {
     expect(isTestPath("src/widget.rs")).toBe(false);
   });
 
+  it("detects pytest's default test_*.py prefix convention, not just the *_test.py suffix", () => {
+    expect(isTestPath("mypackage/test_utils.py")).toBe(true); // pytest default, sitting next to source
+    expect(isTestPath("src/app/test_auth.py")).toBe(true);
+    expect(isTestPath("test_top_level.py")).toBe(true); // repo-root test file
+    expect(isTestPath("internal/cache_test.py")).toBe(true); // the pre-existing suffix form still matches
+    expect(isTestPath("src/app/latest_config.py")).toBe(false); // `test_` mid-segment ⇒ not a test
+    expect(isTestPath("src/app/testing.py")).toBe(false); // no `test_` boundary ⇒ not a test
+  });
+
   it("does not treat framework or integration directory names alone as test evidence", () => {
     expect(isTestPath("src/integration/auth.ts")).toBe(false);
     expect(isTestPath("src/playwright/client.ts")).toBe(false);