diff --git a/actions/parse-ci-reports/src/parsers/CheckStyleParser.test.js b/actions/parse-ci-reports/src/parsers/CheckStyleParser.test.js
new file mode 100644
index 0000000..60898ba
--- /dev/null
+++ b/actions/parse-ci-reports/src/parsers/CheckStyleParser.test.js
@@ -0,0 +1,60 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { CheckStyleParser } from "./CheckStyleParser.js";
+
+const EMPTY_CHECKSTYLE_XML = `<?xml version="1.0" encoding="UTF-8"?>
+<checkstyle version="10.0"></checkstyle>`;
+
+const CHECKSTYLE_WITH_ISSUES_XML = `<?xml version="1.0" encoding="UTF-8"?>
+<checkstyle version="10.0">
+	<file name="src/index.js">
+		<error line="5" column="1" severity="warning" message="Unexpected console statement" source="no-console"/>
+	</file>
+</checkstyle>`;
+
+describe("CheckStyleParser", () => {
+	it("keeps auto-pattern path detection synchronized", () => {
+		const parser = new CheckStyleParser();
+		const filePath = "application/humanize-checkstyle-result.xml";
+
+		assert.ok(parser.matchesAutoPatterns(filePath));
+		assert.ok(parser.canParse(filePath, EMPTY_CHECKSTYLE_XML));
+	});
+
+	it("identifies valid checkstyle XML reports without file entries", () => {
+		const parser = new CheckStyleParser();
+
+		assert.ok(
+			parser.canParse(
+				"application/humanize-report-checkstyle.xml",
+				EMPTY_CHECKSTYLE_XML,
+			),
+		);
+	});
+
+	it("parses empty checkstyle reports as zero lint issues", () => {
+		const parser = new CheckStyleParser();
+
+		const reportData = parser.parse(
+			EMPTY_CHECKSTYLE_XML,
+			"application/humanize-report-checkstyle.xml",
+		);
+		assert.strictEqual(reportData.lintIssues.length, 0);
+	});
+
+	it("parses checkstyle issues from file entries", () => {
+		const parser = new CheckStyleParser();
+
+		const reportData = parser.parse(
+			CHECKSTYLE_WITH_ISSUES_XML,
+			"checkstyle-result.xml",
+		);
+
+		assert.strictEqual(reportData.lintIssues.length, 1);
+		assert.strictEqual(reportData.lintIssues[0].file, "src/index.js");
+		assert.strictEqual(reportData.lintIssues[0].line, 5);
+		assert.strictEqual(reportData.lintIssues[0].column, 1);
+		assert.strictEqual(reportData.lintIssues[0].severity, "warning");
+		assert.strictEqual(reportData.lintIssues[0].rule, "no-console");
+	});
+});
diff --git a/actions/parse-ci-reports/src/parsers/CoberturaParser.test.js b/actions/parse-ci-reports/src/parsers/CoberturaParser.test.js
new file mode 100644
index 0000000..fcc2e0a
--- /dev/null
+++ b/actions/parse-ci-reports/src/parsers/CoberturaParser.test.js
@@ -0,0 +1,46 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { CoberturaParser } from "./CoberturaParser.js";
+
+const SAMPLE_COBERTURA_XML = `<?xml version="1.0"?>
+<coverage line-rate="0.75" branch-rate="0.5">
+	<packages>
+		<package name="app">
+			<classes>
+				<class name="App" filename="src/app.js">
+					<lines>
+						<line number="1" hits="1"/>
+						<line number="2" hits="0"/>
+					</lines>
+				</class>
+			</classes>
+		</package>
+	</packages>
+</coverage>`;
+
+describe("CoberturaParser", () => {
+	it("keeps auto-pattern path detection synchronized", () => {
+		const parser = new CoberturaParser();
+		const filePath = "coverage/humanize-coverage.xml";
+
+		assert.ok(parser.matchesAutoPatterns(filePath));
+		assert.ok(parser.canParse(filePath, SAMPLE_COBERTURA_XML));
+	});
+
+	it("identifies Cobertura XML reports", () => {
+		const parser = new CoberturaParser();
+
+		assert.ok(parser.canParse("coverage/coverage.xml", SAMPLE_COBERTURA_XML));
+		assert.ok(!parser.canParse("reports/report.txt", SAMPLE_COBERTURA_XML));
+	});
+
+	it("parses coverage totals", () => {
+		const parser = new CoberturaParser();
+		const reportData = parser.parse(SAMPLE_COBERTURA_XML, "coverage.xml");
+
+		assert.ok(reportData.coverage);
+		assert.strictEqual(reportData.coverage.lines.total, 2);
+		assert.strictEqual(reportData.coverage.lines.covered, 1);
+		assert.strictEqual(reportData.coverage.lines.percentage, 50);
+	});
+});
diff --git a/actions/parse-ci-reports/src/parsers/ESLintParser.test.js b/actions/parse-ci-reports/src/parsers/ESLintParser.test.js
new file mode 100644
index 0000000..35f9551
--- /dev/null
+++ b/actions/parse-ci-reports/src/parsers/ESLintParser.test.js
@@ -0,0 +1,51 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { ESLintParser } from "./ESLintParser.js";
+
+const SAMPLE_ESLINT_JSON = JSON.stringify([
+	{
+		filePath: "src/app.js",
+		messages: [
+			{
+				ruleId: "no-console",
+				severity: 2,
+				message: "Unexpected console statement.",
+				line: 3,
+				column: 1,
+			},
+		],
+	},
+]);
+
+describe("ESLintParser", () => {
+	it("keeps auto-pattern path detection synchronized", () => {
+		const parser = new ESLintParser();
+		const filePath = "reports/humanize-eslint-report.json";
+
+		assert.ok(parser.matchesAutoPatterns(filePath));
+		assert.ok(parser.canParse(filePath, SAMPLE_ESLINT_JSON));
+	});
+
+	it("identifies ESLint report format", () => {
+		const parser = new ESLintParser();
+
+		assert.ok(parser.canParse("eslint-report.json", SAMPLE_ESLINT_JSON));
+		assert.ok(!parser.canParse("eslint-report.txt", SAMPLE_ESLINT_JSON));
+		assert.ok(!parser.canParse("eslint-report.json", "{}"));
+	});
+
+	it("parses lint issues from ESLint JSON", () => {
+		const parser = new ESLintParser();
+		const reportData = parser.parse(SAMPLE_ESLINT_JSON, "eslint-report.json");
+
+		assert.strictEqual(reportData.lintIssues.length, 1);
+		const [issue] = reportData.lintIssues;
+
+		assert.strictEqual(issue.file, "src/app.js");
+		assert.strictEqual(issue.line, 3);
+		assert.strictEqual(issue.column, 1);
+		assert.strictEqual(issue.severity, "error");
+		assert.strictEqual(issue.rule, "no-console");
+		assert.strictEqual(issue.message, "Unexpected console statement.");
+	});
+});
diff --git a/actions/parse-ci-reports/src/parsers/LCOVParser.test.js b/actions/parse-ci-reports/src/parsers/LCOVParser.test.js
new file mode 100644
index 0000000..6fbaa19
--- /dev/null
+++ b/actions/parse-ci-reports/src/parsers/LCOVParser.test.js
@@ -0,0 +1,43 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { LCOVParser } from "./LCOVParser.js";
+
+const SAMPLE_LCOV = `TN:
+SF:src/app.js
+DA:1,1
+DA:2,0
+FNDA:1,handler
+BRDA:2,0,0,1
+BRDA:2,0,1,0
+end_of_record
+`;
+
+describe("LCOVParser", () => {
+	it("keeps auto-pattern path detection synchronized", () => {
+		const parser = new LCOVParser();
+		const filePath = "coverage/humanize-lcov.info";
+
+		assert.ok(parser.matchesAutoPatterns(filePath));
+		assert.ok(parser.canParse(filePath, SAMPLE_LCOV));
+	});
+
+	it("identifies LCOV reports", () => {
+		const parser = new LCOVParser();
+
+		assert.ok(parser.canParse("coverage/lcov.info", SAMPLE_LCOV));
+		assert.ok(!parser.canParse("coverage/report.txt", SAMPLE_LCOV));
+	});
+
+	it("parses line, function, and branch coverage", () => {
+		const parser = new LCOVParser();
+		const reportData = parser.parse(SAMPLE_LCOV, "lcov.info");
+
+		assert.ok(reportData.coverage);
+		assert.strictEqual(reportData.coverage.lines.total, 2);
+		assert.strictEqual(reportData.coverage.lines.covered, 1);
+		assert.strictEqual(reportData.coverage.functions.total, 1);
+		assert.strictEqual(reportData.coverage.functions.covered, 1);
+		assert.strictEqual(reportData.coverage.branches.total, 2);
+		assert.strictEqual(reportData.coverage.branches.covered, 1);
+	});
+});