test(scan): add marble tests for scan

for whatever reason, we had zero tests for scan. :(

spec/operators/scan-spec.js

@@ -0,0 +1,107 @@
+/* globals describe, it, expect, expectObservable, hot */
+var Rx = require('../../dist/cjs/Rx');
+var Observable = Rx.Observable;
+
+describe('Observable.prototype.scan()', function () {
+  it('should scan things', function () {
+    var e1 = hot('--a--^--b--c--d--e--f--g--|');
+    var expected =    '---u--v--w--x--y--z--|';
+
+    var values = {
+      u: ['b'],
+      v: ['b', 'c'],
+      w: ['b', 'c', 'd'],
+      x: ['b', 'c', 'd', 'e'],
+      y: ['b', 'c', 'd', 'e', 'f'],
+      z: ['b', 'c', 'd', 'e', 'f', 'g']
+    };
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source).toBe(expected, values);
+  });
+
+  it('should handle errors', function () {
+    var e1 = hot('--a--^--b--c--d--#');
+    var expected =    '---u--v--w--#';
+
+    var values = {
+      u: ['b'],
+      v: ['b', 'c'],
+      w: ['b', 'c', 'd']
+    };
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source).toBe(expected, values);
+  })
+
+  it('should handle errors in the projection function', function () {
+    var e1 = hot('--a--^--b--c--d--e--f--g--|');
+    var expected =    '---u--v--#';
+
+    var values = {
+      u: ['b'],
+      v: ['b', 'c'],
+      w: ['b', 'c', 'd'],
+      x: ['b', 'c', 'd', 'e'],
+      y: ['b', 'c', 'd', 'e', 'f'],
+      z: ['b', 'c', 'd', 'e', 'f', 'g']
+    };
+
+    var source = e1.scan(function (acc, x) {
+      if (x === 'd') {
+        throw 'bad!';
+      }
+      return [].concat(acc, x);
+    }, []);
+
+    expectObservable(source).toBe(expected, values, 'bad!');
+  })
+
+  it('handle empty', function () {
+    var e1 = Observable.empty();
+    var expected = '|';
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source).toBe(expected);
+  });
+
+  it('handle never', function () {
+    var e1 = Observable.never();
+    var expected = '-';
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source).toBe(expected);
+  });
+
+  it('handle throw', function () {
+    var e1 = Observable.throw('bad!');
+    var expected = '#';
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source).toBe(expected, undefined, 'bad!');
+  });
+
+  it('should scan unsubscription', function () {
+    var e1 = hot('--a--^--b--c--d--e--f--g--|');
+    var expected =    '---u--v--w--x--';
+    var sub =         '^             !';
+    var values = {
+      u: ['b'],
+      v: ['b', 'c'],
+      w: ['b', 'c', 'd'],
+      x: ['b', 'c', 'd', 'e'],
+      y: ['b', 'c', 'd', 'e', 'f'],
+      z: ['b', 'c', 'd', 'e', 'f', 'g']
+    };
+
+    var source = e1.scan(function (acc, x) { return [].concat(acc, x); }, []);
+
+    expectObservable(source, sub).toBe(expected, values);
+  });
+
+});