diff --git a/test/util.test.mjs b/test/util.test.mjs
new file mode 100644
index 00000000..679c922b
--- /dev/null
+++ b/test/util.test.mjs
@@ -0,0 +1,60 @@
+import { strict as assert } from 'assert';
+import { isNote, tokenizeNote, toMidi } from '../util.mjs';
+
+describe('isNote', () => {
+  it('should recognize notes without accidentals', function () {
+    'C3 D3 E3 F3 G3 A3 B3 C4 D5 c5 d5 e5'.split(' ').forEach((note) => {
+      assert.equal(isNote(note), true);
+    });
+  });
+  it('should recognize notes with accidentals', function () {
+    'C#3 D##3 Eb3 Fbb3 Bb5'.split(' ').forEach((note) => {
+      assert.equal(isNote(note), true);
+    });
+  });
+  it('should not recognize invalid notes', function () {
+    assert.equal(isNote('H5'), false);
+    assert.equal(isNote('C'), false);
+    assert.equal(isNote('X'), false);
+    assert.equal(isNote(1), false);
+  });
+});
+
+describe('isNote', () => {
+  it('should tokenize notes without accidentals', function () {
+    assert.deepStrictEqual(tokenizeNote('C3'), ['C', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('D3'), ['D', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('E3'), ['E', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('F3'), ['F', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('G3'), ['G', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('A3'), ['A', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('B3'), ['B', '', '3']);
+    assert.deepStrictEqual(tokenizeNote('C4'), ['C', '', '4']);
+    assert.deepStrictEqual(tokenizeNote('D5'), ['D', '', '5']);
+  });
+  it('should tokenize notes with accidentals', function () {
+    assert.deepStrictEqual(tokenizeNote('C#3'), ['C', '#', '3']);
+    assert.deepStrictEqual(tokenizeNote('D##3'), ['D', '##', '3']);
+    assert.deepStrictEqual(tokenizeNote('Eb3'), ['E', 'b', '3']);
+    assert.deepStrictEqual(tokenizeNote('Fbb3'), ['F', 'bb', '3']);
+    assert.deepStrictEqual(tokenizeNote('Bb5'), ['B', 'b', '5']);
+  });
+  it('should note tokenize invalid notes', function () {
+    assert.deepStrictEqual(tokenizeNote('X'), []);
+    assert.deepStrictEqual(tokenizeNote('asfasf'), []);
+    assert.deepStrictEqual(tokenizeNote(123), []);
+  });
+});
+describe('toMidi', () => {
+  it('should turn notes into midi', function () {
+    assert.equal(toMidi('A4'), 69);
+    assert.equal(toMidi('C4'), 60);
+    assert.equal(toMidi('Db4'), 61);
+    assert.equal(toMidi('C3'), 48);
+    assert.equal(toMidi('Cb3'), 47);
+    assert.equal(toMidi('Cbb3'), 46);
+    assert.equal(toMidi('C#3'), 49);
+    assert.equal(toMidi('C#3'), 49);
+    assert.equal(toMidi('C##3'), 50);
+  });
+});
diff --git a/util.mjs b/util.mjs
index 0702c23b..0f501a91 100644
--- a/util.mjs
+++ b/util.mjs
@@ -1,7 +1,16 @@
-export const isNote = (name) => /^[a-gA-G][#b]?[0-9]$/.test(name);
-export const tokenizeNote = (note) => note.match(/^([a-gA-G])([#b])?([0-9])?$/).slice(1);
+export const isNote = (name) => /^[a-gA-G][#b]*[0-9]$/.test(name);
+export const tokenizeNote = (note) =>
+  typeof note === 'string'
+    ? note
+        .match(/^([a-gA-G])([#b]*)([0-9])?$/)
+        ?.slice(1)
+        ?.map((x) => (x === undefined ? '' : x)) || []
+    : [];
 export const toMidi = (note) => {
   const [pc, acc, oct] = tokenizeNote(note);
+  if (!pc) {
+    throw new Error('not a note: "' + note + '"');
+  }
   const chroma = { c: 0, d: 2, e: 4, f: 5, g: 7, a: 9, b: 11 }[pc.toLowerCase()];
   const offset = acc?.split('').reduce((o, char) => o + { '#': 1, b: -1 }[char], 0) || 0;
   return (Number(oct) + 1) * 12 + chroma + offset;