jest: Patch implicit else branch coverage

Author: bertschneider

packages/jest-runner/index.ts

@@ -17,6 +17,7 @@
 import type { JestEnvironment } from "@jest/environment";
 import { TestResult } from "@jest/test-result";
 import { Config } from "@jest/types";
+import * as libCoverage from "istanbul-lib-coverage";
 import * as reports from "istanbul-reports";
 import Runtime from "jest-runtime";
 
@@ -71,6 +72,7 @@ export default async function jazzerTestRunner(
 		testPath,
 		sendMessageToJest,
 	).then((result: TestResult) => {
+		includeImplicitElseBranches(environment.global.__coverage__);
 		return cleanupTestResultDetails(result);
 	});
 }
@@ -90,6 +92,52 @@ function cleanupTestResultDetails(result: TestResult) {
 	return result;
 }
 
+/**
+ * Coverage fix from https://github.com/vitest-dev/vitest/pull/2275
+ * In our tests this seems to only affect the coverage of TypeScript files,
+ * hence including the fix in jest-runner should be sufficient.
+ *
+ * Original comment:
+ * Work-around for #1887 and #2239 while waiting for https://github.com/istanbuljs/istanbuljs/pull/706
+ * Goes through all files in the coverage map and checks if branchMap's have
+ * if-statements with implicit else. When finds one, copies source location of
+ * the if-statement into the else statement.
+ */
+export function includeImplicitElseBranches(
+	coverageMapData: libCoverage.CoverageMapData,
+) {
+	if (!coverageMapData) {
+		return;
+	}
+	function isEmptyCoverageRange(range: libCoverage.Range) {
+		return (
+			range.start === undefined ||
+			range.start.line === undefined ||
+			range.start.column === undefined ||
+			range.end === undefined ||
+			range.end.line === undefined ||
+			range.end.column === undefined
+		);
+	}
+	const coverageMap = libCoverage.createCoverageMap(coverageMapData);
+	for (const file of coverageMap.files()) {
+		const fileCoverage = coverageMap.fileCoverageFor(file);
+		for (const branchMap of Object.values(fileCoverage.branchMap)) {
+			if (branchMap.type === "if") {
+				const lastIndex = branchMap.locations.length - 1;
+				if (lastIndex > 0) {
+					const elseLocation = branchMap.locations[lastIndex];
+					if (elseLocation && isEmptyCoverageRange(elseLocation)) {
+						const ifLocation = branchMap.locations[0];
+						elseLocation.start = { ...ifLocation.start };
+						elseLocation.end = { ...ifLocation.end };
+					}
+				}
+			}
+		}
+	}
+}
+
 // Global definition of the Jest fuzz test extension function.
 // This is required to allow the Typescript compiler to recognize it.
 declare global {

tests/code_coverage/sample_fuzz_test/expected_coverage/fuzz+lib+codeCoverage-fuzz.json

@@ -104,7 +104,10 @@
 						"start": { "line": 24, "column": 1 },
 						"end": { "line": 26, "column": 2 }
 					},
-					{ "start": {}, "end": {} }
+					{
+						"start": { "line": 24, "column": 1 },
+						"end": { "line": 26, "column": 2 }
+					}
 				],
 				"line": 24
 			}
@@ -164,7 +167,10 @@
 						"start": { "line": 19, "column": 1 },
 						"end": { "line": 21, "column": 2 }
 					},
-					{ "start": {}, "end": {} }
+					{
+						"start": { "line": 19, "column": 1 },
+						"end": { "line": 21, "column": 2 }
+					}
 				],
 				"line": 19
 			}

tests/code_coverage/sample_fuzz_test/expected_coverage/fuzz+lib+otherCodeCoverage-fuzz.json

@@ -113,7 +113,10 @@
 						"start": { "line": 24, "column": 1 },
 						"end": { "line": 26, "column": 2 }
 					},
-					{ "start": {}, "end": {} }
+					{
+						"start": { "line": 24, "column": 1 },
+						"end": { "line": 26, "column": 2 }
+					}
 				],
 				"line": 24
 			}
@@ -173,7 +176,10 @@
 						"start": { "line": 19, "column": 1 },
 						"end": { "line": 21, "column": 2 }
 					},
-					{ "start": {}, "end": {} }
+					{
+						"start": { "line": 19, "column": 1 },
+						"end": { "line": 21, "column": 2 }
+					}
 				],
 				"line": 19
 			}

tests/helpers.js

@@ -426,7 +426,7 @@ class FuzzTestBuilder {
 	}
 
 	coverage(coverage) {
-		this._coverage = coverage;
+		this._coverage = coverage === undefined ? true : coverage;
 		return this;
 	}
 

tests/jest_integration/integration.test.js

@@ -472,6 +472,27 @@ describe("Jest TS integration", () => {
 			});
 		});
 	});
+
+	describe("Regression mode", () => {
+		const regressionTestBuilder = new FuzzTestBuilder()
+			.dir(projectDir)
+			.jestTestFile(jestTsTestFile + ".ts");
+
+		describe("mixed features", () => {
+			it("cover implicit else branch", async () => {
+				regressionTestBuilder
+					.jestTestName("execute sync test")
+					.coverage()
+					.build()
+					.execute();
+				const coverage = readCoverageOf(projectDir, "target.ts");
+				// Expect that every branch has two entries, one for the if and one for the else branch.
+				Object.keys(coverage.b).forEach((branch) => {
+					expect(coverage.b[branch]).toHaveLength(2);
+				});
+			});
+		});
+	});
 });
 
 // Deflake the "timeout after N seconds" test to be more tolerant to small variations of N (+-1).
@@ -513,3 +534,18 @@ function cleanupProjectFiles(projectDir, jestTestFile) {
 		});
 	};
 }
+
+function readCoverageOf(projectDir, fileName) {
+	const report = JSON.parse(
+		fs.readFileSync(
+			path.join(projectDir, "coverage", "coverage-final.json"),
+			"utf-8",
+		),
+	);
+	for (let path of Object.keys(report)) {
+		if (path.endsWith(fileName)) {
+			return report[path];
+		}
+	}
+	throw new Error("Could not find coverage for " + fileName);
+}

tests/jest_integration/jest_project_ts/target.ts

@@ -15,9 +15,15 @@
  */
 
 export function fuzzMe(data: Buffer) {
-	if (data.toString() === "Awesome") {
-		throw Error("Welcome to Awesome Fuzzing!");
+	if (typeof data === "object") {
+		if (data.toString() === "Awesome") {
+			throw Error("Welcome to Awesome Fuzzing!");
+		}
+		return data;
 	}
+	// Implicit else block to test coverage error,
+	// see: https://github.com/vitest-dev/vitest/pull/2275
+	return data;
 }
 
 export function callbackFuzzMe(data: Buffer, done: (e?: Error) => void) {