diff --git a/Makefile b/Makefile
index e903db7..45daa10 100755
--- a/Makefile
+++ b/Makefile
@@ -95,7 +95,9 @@ test-examples: ## run medium (feature) tests
 
 test-bundle: ## run small (unit) tests
 test-bundle: build-bundle
-	$(NODE_BIN)/nyc --reporter=lcov --reporter=text-summary --report-dir="$(TARGET_PATH)/coverage" --exclude-after-remap $(NODE_BIN)/mocha $(TARGET_PATH)/test.js
+	$(NODE_BIN)/nyc --report-dir="$(TARGET_PATH)/coverage" --exclude-after-remap \
+		--reporter=html --reporter=lcov --reporter=text-summary \
+		$(NODE_BIN)/mocha $(TARGET_PATH)/test.js
 
 test-rules: ## validate the rules directory
 test-rules: build-bundle
diff --git a/config/rollup.js b/config/rollup.js
index 7655fc9..35f9839 100644
--- a/config/rollup.js
+++ b/config/rollup.js
@@ -76,6 +76,7 @@ const bundle = {
 					'intersection',
 					'isNil',
 					'isString',
+					'kebabCase',
 				],
 				'node_modules/noicejs/out/main-bundle.js': [
 					'BaseError',
diff --git a/src/rule.ts b/src/rule.ts
index 924bf9b..d539a0b 100644
--- a/src/rule.ts
+++ b/src/rule.ts
@@ -74,7 +74,7 @@ export async function loadRules(paths: Array<string>, ctx: VisitorContext): Prom
         ctx.addSchema(data.name, data.definitions);
       }
 
-      rules.push(...data.rules.map((data: any) => new Rule(data)));
+      rules.push(...data.rules.map((data: RuleData) => new Rule(data)));
     }
   }
 
diff --git a/test/error/TestError.ts b/test/error/TestError.ts
new file mode 100644
index 0000000..1fa6c39
--- /dev/null
+++ b/test/error/TestError.ts
@@ -0,0 +1,34 @@
+import { expect } from 'chai';
+import { kebabCase } from 'lodash';
+
+import { InvalidArgumentError } from '../../src/error/InvalidArgumentError';
+import { NotFoundError } from '../../src/error/NotFoundError';
+
+const errors = [
+  InvalidArgumentError,
+  NotFoundError,
+];
+
+describe('errors', () => {
+  for (const errorType of errors) {
+    describe(kebabCase(errorType.name), () => {
+      it('should have a message', () => {
+        const err = new errorType();
+        expect(err.message).to.not.equal('');
+      });
+
+      it('should include nested errors in the stack trace', () => {
+        const inner = new Error('inner error');
+        const err = new errorType('outer error', inner);
+        expect(err.stack).to.include('inner', 'inner error message').and.include('outer', 'outer error message');
+      });
+
+      it('should have the nested error', () => {
+        const inner = new Error('inner error');
+        const err = new errorType('outer error', inner);
+        expect(err.cause()).to.equal(inner);
+        expect(err.length).to.equal(1);
+      });
+    });
+  }
+});
diff --git a/test/utils/ajv/TestFriendlyErrors.ts b/test/utils/ajv/TestFriendlyErrors.ts
new file mode 100644
index 0000000..d74afa3
--- /dev/null
+++ b/test/utils/ajv/TestFriendlyErrors.ts
@@ -0,0 +1,15 @@
+import { expect } from 'chai';
+
+import { friendlyError } from '../../../src/utils/ajv';
+
+describe('friendly errors', () => {
+  it('should have a message', () => {
+    const err = friendlyError({
+      keyword: 'test',
+      dataPath: 'test-path',
+      schemaPath: 'test-path',
+      params: { /* ? */ },
+    });
+    expect(err.msg).to.not.equal('');
+  });
+});