Prepend option names with opts. in error messages

src/index.js

@@ -6,7 +6,7 @@ const validateOpts = (opts, chunkMultiple) => {
 	opts.chunkSize = Math.ceil(opts.chunkSize / chunkMultiple) * chunkMultiple;
 
 	if (opts.chunkSize === 0) {
-		throw new Error('chunkSize must be larger than 0');
+		throw new Error('opts.chunkSize must be larger than 0');
 	}
 
 	return opts;
@@ -17,7 +17,7 @@ const b64 = (input, opts) => {
 		return b64[opts.method](input, opts);
 	}
 
-	return Promise.reject(new Error('method must be \'encode\' or \'decode\'.'));
+	return Promise.reject(new Error('opts.method must be \'encode\' or \'decode\'.'));
 };
 
 b64.encode = (input, opts) => new Promise(resolve => {

test/b64.decode.js

@@ -31,7 +31,7 @@ test('b64.decode rounds chunks up to multiples of 4', async t => {
 
 test('b64.decode rejects Promise if chunkSize is 0', async t => {
 	const error = 	await t.throws(b64.decode(values.string, { chunkSize: 0 }));
-	t.is(error.message, 'chunkSize must be larger than 0');
+	t.is(error.message, 'opts.chunkSize must be larger than 0');
 });
 
 test('b64.decode rejects Promise if input is not a string', async t => {

test/b64.encode.js

@@ -28,7 +28,7 @@ test('b64.encode rounds chunks up to multiples of 3', async t => {
 
 test('b64.encode rejects Promise if chunkSize is 0', async t => {
 	const error = await t.throws(b64.encode(values.buffer, { chunkSize: 0 }));
-	t.is(error.message, 'chunkSize must be larger than 0');
+	t.is(error.message, 'opts.chunkSize must be larger than 0');
 });
 
 test('b64.encode rejects Promise if input is not a buffer', async t => {

test/b64.js

@@ -16,5 +16,5 @@ test('b64 calls b64[opts.method]', async t => {
 
 test('b64 rejects Promise if method is not \'encode\' or \'decode\'', async t => {
 	const error = await t.throws(b64(values.buffer));
-	t.is(error.message, 'method must be \'encode\' or \'decode\'.');
+	t.is(error.message, 'opts.method must be \'encode\' or \'decode\'.');
 });