Add "to start with" as an alias for "to begin with".

lib/assertions.js

@@ -687,7 +687,10 @@ module.exports = expect => {
   });
 
   expect.addAssertion(
-    '<string> [not] to begin with <string>',
+    [
+      '<string> [not] to begin with <string>',
+      '<string> [not] to start with <string>'
+    ],
     (expect, subject, value) => {
       if (value === '') {
         throw new Error(

test/assertions/to-start-with.spec.js

@@ -0,0 +1,44 @@
+/*global expect*/
+describe('to start with assertion', function() {
+  it('should throw an error when the expected prefix is the empty string', function() {
+    expect(
+      function() {
+        expect('foo', 'to start with', '');
+      },
+      'to throw',
+      "The 'to start with' assertion does not support a prefix of the empty string"
+    );
+  });
+
+  describe('without the "not" flag', function() {
+    it('asserts equality with a string', function() {
+      expect('hello', 'to start with', 'hello');
+      expect('hello world', 'to start with', 'hello');
+    });
+  });
+
+  describe('when the assertion fails', function() {
+    it('does not include a diff when there is no common prefix', function() {
+      expect(
+        function() {
+          expect('hello world', 'to start with', 'foo');
+        },
+        'to throw exception',
+        "expected 'hello world' to start with 'foo'"
+      );
+    });
+
+    it('includes a diff when there is a common prefix', function() {
+      expect(
+        function() {
+          expect('hello world', 'to start with', 'hell yeah');
+        },
+        'to throw exception',
+        "expected 'hello world' to start with 'hell yeah'\n" +
+          '\n' +
+          'hello world\n' +
+          '^^^^'
+      );
+    });
+  });
+});