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diff --git a/test/index_test.ts b/test/index_test.ts
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+import mitt, { Emitter } from '..';
+import chai, { expect } from 'chai';
+import { spy } from 'sinon';
+import sinonChai from 'sinon-chai';
+chai.use(sinonChai);
+
+describe('mitt', () => {
+	it('should default export be a function', () => {
+		expect(mitt).to.be.a('function');
+	});
+
+	it('should accept an optional event handler map', () => {
+		expect(() => mitt(new Map())).not.to.throw;
+		const map = new Map();
+		const a = spy();
+		const b = spy();
+		map.set('foo', [a, b]);
+		const events = mitt(map);
+		events.emit('foo');
+		expect(a).to.have.been.calledOnce;
+		expect(b).to.have.been.calledOnce;
+	});
+});
+
+describe('mitt#', () => {
+	let events, inst: Emitter;
+
+	beforeEach( () => {
+		events = new Map();
+		inst = mitt(events);
+	});
+
+	describe('properties', () => {
+		it('should expose the event handler map', () => {
+			expect(inst)
+				.to.have.property('all')
+				.that.is.a('map');
+		});
+	});
+
+	describe('on()', () => {
+		it('should be a function', () => {
+			expect(inst)
+				.to.have.property('on')
+				.that.is.a('function');
+		});
+
+		it('should register handler for new type', () => {
+			const foo = () => {};
+			inst.on('foo', foo);
+
+			expect(events.get('foo')).to.deep.equal([foo]);
+		});
+
+		it('should register handlers for any type strings', () => {
+			const foo = () => {};
+			inst.on('constructor', foo);
+
+			expect(events.get('constructor')).to.deep.equal([foo]);
+		});
+
+		it('should append handler for existing type', () => {
+			const foo = () => {};
+			const bar = () => {};
+			inst.on('foo', foo);
+			inst.on('foo', bar);
+
+			expect(events.get('foo')).to.deep.equal([foo, bar]);
+		});
+
+		it('should NOT normalize case', () => {
+			const foo = () => {};
+			inst.on('FOO', foo);
+			inst.on('Bar', foo);
+			inst.on('baz:baT!', foo);
+
+			expect(events.get('FOO')).to.deep.equal([foo]);
+			expect(events.has('foo')).to.equal(false);
+			expect(events.get('Bar')).to.deep.equal([foo]);
+			expect(events.has('bar')).to.equal(false);
+			expect(events.get('baz:baT!')).to.deep.equal([foo]);
+		});
+
+		it('can take symbols for event types', () => {
+			const foo = () => {};
+			const eventType = Symbol('eventType');
+			inst.on(eventType, foo);
+			expect(events.get(eventType)).to.deep.equal([foo]);
+		});
+
+		// Adding the same listener multiple times should register it multiple times.
+		// See https://nodejs.org/api/events.html#events_emitter_on_eventname_listener
+		it('should add duplicate listeners', () => {
+			const foo = () => {};
+			inst.on('foo', foo);
+			inst.on('foo', foo);
+			expect(events.get('foo')).to.deep.equal([foo, foo]);
+		});
+	});
+
+	describe('off()', () => {
+		it('should be a function', () => {
+			expect(inst)
+				.to.have.property('off')
+				.that.is.a('function');
+		});
+
+		it('should remove handler for type', () => {
+			const foo = () => {};
+			inst.on('foo', foo);
+			inst.off('foo', foo);
+
+			expect(events.get('foo')).to.be.empty;
+		});
+
+		it('should NOT normalize case', () => {
+			const foo = () => {};
+			inst.on('FOO', foo);
+			inst.on('Bar', foo);
+			inst.on('baz:bat!', foo);
+
+			inst.off('FOO', foo);
+			inst.off('Bar', foo);
+			inst.off('baz:baT!', foo);
+
+			expect(events.get('FOO')).to.be.empty;
+			expect(events.has('foo')).to.equal(false);
+			expect(events.get('Bar')).to.be.empty;
+			expect(events.has('bar')).to.equal(false);
+			expect(events.get('baz:bat!')).to.have.lengthOf(1);
+		});
+
+		it('should remove only the first matching listener', () => {
+			const foo = () => {};
+			inst.on('foo', foo);
+			inst.on('foo', foo);
+			inst.off('foo', foo);
+			expect(events.get('foo')).to.deep.equal([foo]);
+			inst.off('foo', foo);
+			expect(events.get('foo')).to.deep.equal([]);
+		});
+	});
+
+	describe('emit()', () => {
+		it('should be a function', () => {
+			expect(inst)
+				.to.have.property('emit')
+				.that.is.a('function');
+		});
+
+		it('should invoke handler for type', () => {
+			const event = { a: 'b' };
+
+			inst.on('foo', (one, two?) => {
+				expect(one).to.deep.equal(event);
+				expect(two).to.be.an('undefined');
+			});
+
+			inst.emit('foo', event);
+		});
+
+		it('should NOT ignore case', () => {
+			const onFoo = spy(),
+				onFOO = spy();
+			events.set('Foo', [onFoo]);
+			events.set('FOO', [onFOO]);
+
+			inst.emit('Foo', 'Foo arg');
+			inst.emit('FOO', 'FOO arg');
+
+			expect(onFoo).to.have.been.calledOnce.and.calledWith('Foo arg');
+			expect(onFOO).to.have.been.calledOnce.and.calledWith('FOO arg');
+		});
+
+		it('should invoke * handlers', () => {
+			const star = spy(),
+				ea = { a: 'a' },
+				eb = { b: 'b' };
+
+			events.set('*', [star]);
+
+			inst.emit('foo', ea);
+			expect(star).to.have.been.calledOnce.and.calledWith('foo', ea);
+			star.resetHistory();
+
+			inst.emit('bar', eb);
+			expect(star).to.have.been.calledOnce.and.calledWith('bar', eb);
+		});
+	});
+});