added ability to revert (#21)

tests/unit/domain/Script.spec.ts

@@ -3,15 +3,44 @@ import { expect } from 'chai';
 import { Script } from '@/domain/Script';
 
 describe('Script', () => {
-
-    it('cannot construct with duplicate lines', () => {
-        // arrange
-        const code = 'duplicate\nduplicate\ntest\nduplicate';
-
-        // act
-        function construct() { return new Script('ScriptName', code, [], true); }
-
-        // assert
-        expect(construct).to.throw();
+    describe('ctor', () => {
+        describe('code', () => {
+            it('cannot construct with duplicate lines', () => {
+                const code = 'duplicate\nduplicate\ntest\nduplicate';
+                expect(() => createWithCode(code)).to.throw();
+            });
+            it('cannot construct with empty lines', () => {
+                const code = 'duplicate\n\n\ntest\nduplicate';
+                expect(() => createWithCode(code)).to.throw();
+            });
+        });
+        describe('revertCode', () => {
+            it('cannot construct with duplicate lines', () => {
+                const code = 'duplicate\nduplicate\ntest\nduplicate';
+                expect(() => createWithCode('REM', code)).to.throw();
+            });
+            it('cannot construct with empty lines', () => {
+                const code = 'duplicate\n\n\ntest\nduplicate';
+                expect(() => createWithCode('REM', code)).to.throw();
+            });
+            it('cannot construct with when same as code', () => {
+                const code = 'REM';
+                expect(() => createWithCode(code, code)).to.throw();
+            });
+        });
+        describe('canRevert', () => {
+            it('returns false without revert code', () => {
+                const sut = createWithCode('code');
+                expect(sut.canRevert()).to.equal(false);
+            });
+            it('returns true with revert code', () => {
+                const sut = createWithCode('code', 'non empty revert code');
+                expect(sut.canRevert()).to.equal(true);
+            });
+        });
     });
 });
+
+function createWithCode(code: string, revertCode?: string): Script {
+    return new Script('name', code, revertCode, [], false);
+}