Add issue 51 (#53)

Author: renatomariscal

spec/issues/51.test.ts

@@ -0,0 +1,21 @@
+import test from 'ava';
+
+import { Substitute, Arg } from '../../src/index';
+
+interface ICalculator {
+    add(a: number, b: number): number;
+    divide(a: number, b: number): number;
+}
+test('issue 51 - All functions shares the same state', async t => {
+    const calculator = Substitute.for<ICalculator>();
+    calculator.add(1, 2).returns(4);
+
+    const result = calculator.add(1, 2);
+    t.is(result, 4);
+    try {
+        calculator.received().divide(1, 2);
+        t.fail('Expected to have failed.');
+    } catch (e) {
+        t.regex(e.toString(), /Expected 1 or more calls to the property divide with no arguments/);
+    }
+});