Throw Error on syntax errors

2 files changed, 27 insertions, 2 deletions

diff --git a/__tests__/lexer.test.js b/__tests__/lexer.test.js
index 38c880e..b9260b8 100644
--- a/__tests__/lexer.test.js
+++ b/__tests__/lexer.test.js
@@ -5,8 +5,16 @@ describe('lex', () => {
     expect(lex('')).toEqual([])
   })
 
-  it('signals an error on unexpected input', () => {
-    expect(lex('q')).toBe('error')
+  it('throws on unexpected input', () => {
+    expect(() => { lex('q') }).toThrow(/Syntax error/)
+  })
+
+  it('throws on unexpected input at the end', () => {
+    expect(() => { lex('1d6 `') }).toThrow(/Syntax error/)
+  })
+
+  it('throws on unexpected input in the middle', () => {
+    expect(() => { lex('2d3 + b 3d4') }).toThrow(/Syntax error/)
   })
 
   describe('ignores whitespace', () => {
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 74ca442..f3c6e97 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -1,6 +1,23 @@
 const { parse } = require('../src/parser.js')
 
 describe('parse', () => {
+  describe('error handling', () => {
+    it('throws when a binary operation lacks an argument', () => {
+      expect(() => { parse('1d') }).toThrow(/Syntax error/)
+      expect(() => { parse('2+3+') }).toThrow(/Syntax error/)
+    })
+
+    it('throws when two binary operations follow each other', () => {
+      expect(() => { parse('1dd2') }).toThrow(/Syntax error/)
+      expect(() => { parse('1+d2') }).toThrow(/Syntax error/)
+    })
+
+    it('throws when two dice not combined with a binary operation', () => {
+      expect(() => { parse('(1d4)(1d6)') }).toThrow(/Syntax error/)
+      expect(() => { parse('1 2') }).toThrow(/Syntax error/)
+    })
+  })
+
   it('parses a constant', () => {
     expect(parse('5')).toEqual({ type: 'constant', value: 5 })
   })