test: epsilon rewrite rules

Author: gruhn

test/regex.spec.ts

@@ -207,11 +207,7 @@ describe('size', () => {
 
 describe('rewrite rules', () => {
 
- // TODO:
- // - test intersection/complement rules.
- // - test rules involving epsilon / empty set
- // (can't be tested right now because parser does not
- // support empty set `$.^` and epsilon `()`.
+ // TODO: test intersection/complement rules.
 
  const rewriteCases = [
  // concat rules:
@@ -225,8 +221,6 @@ describe('rewrite rules', () => {
  [/^a?a?$/, /^(a?){2}$/],
  [/^()a$/, /^a$/],
  [/^a()$/, /^a$/],
- // TODO:
- // [/^a($.^)$/, /$.^/],
  // union rules:
  [/^(a|a)$/, /^a$/],
  // expected expression:
@@ -245,12 +239,15 @@ describe('rewrite rules', () => {
  [/^(ba|a)$/, /^b?a$/],
  [/^(a|ab)$/, /^ab?$/],
  [/^(a|ba)$/, /^b?a$/],
+ // union-of-star rules:
+ [/^(a*|)$/, /^a*$/],
  // TODO:
  // [/^(a|a{2}|a{3}|a{4}|a{5})$/, /^(a{1,5})$/],
  // [/^(a|a{2}|a{3}|a{4}|a{5}|b)$/, /^(a{1,5}|b)$/],
  // star rules:
  [/^(a*)*$/, /^a*$/],
  [/^(a*b*)*$/, /^[ab]*$/],
+ [/^()*$/, /^$/],
  ] as const
 
  for (const [source, target] of rewriteCases) {
@@ -275,7 +272,7 @@ describe('derivative', () => {
 
  for (const [input, str, expected] of derivativeCases) {
  it(`of ${input} with respect to "${str}" is ${expected}`, () => {
- const actual = RE.derivative(str, AST.toExtRegex(parseRegExp(input)))
+  const actual = RE.derivative(str, AST.toExtRegex(parseRegExp(input)))
  assert(RE.isStdRegex(actual))
  assert.deepEqual(RE.toRegExp(actual), expected)
  })