Add toContainString and toContainSubstring

This adds the new methods from 2.7.0 without the breaking changes.

src/ExpectObj.hack

@@ -242,6 +242,18 @@ class ExpectObj<T> extends Assert {
     $this->assertContains($needle, not_hack_array($this->var), $msg);
   }
 
+  /**
+   * Assert: $actual contains the substring $expected
+   */
+  public function toContainSubstring(
+    string $expected,
+    string $msg = '',
+    mixed ...$args
+  ): void where T = string {
+    $msg = \vsprintf($msg, $args);
+    $this->assertContains($expected, $this->var, $msg);
+  }
+
   /**
    * Assert: That the KeyedTraversible $key has a key set.
    * Note:   If $key is a Set, use assertContains.
@@ -453,6 +465,14 @@ class ExpectObj<T> extends Assert {
     $this->assertNotContains($expected, not_hack_array($this->var), $msg);
   }
 
+  /**
+   * Assert: $actual does not contain the substring $expected
+   */
+  public function toNotContainSubstring(string $expected, string $msg = '', mixed ...$args): void where T = string {
+    $msg = \vsprintf($msg, $args);
+    $this->assertNotContains($expected, not_hack_array($this->var), $msg);
+  }
+
   /**
    * Assert: That the KeyedTraversible $key has a key set.
    * Note:   If $key is a Set, use assertContains.

tests/ExpectObjTest.hack

@@ -57,6 +57,12 @@ final class ExpectObjTest extends HackTest {
     expect(dict[])->toBeType('KeyedContainer');
     expect(array(1, 2, 3))->toContain(2);
     expect(array(1, 2, 3))->toNotContain(7);
+    expect('foo')->toContain('foo');
+    expect('foo')->toContain('o');
+    expect('foo')->toNotContain('a');
+    expect('foo')->toContainSubstring('foo');
+    expect('foo')->toContainSubstring('o');
+    expect('foo')->toNotContainSubstring('a');
     expect(1)->toAlmostEqual(1);
     expect(null)->toAlmostEqual(null);
 
@@ -151,6 +157,9 @@ final class ExpectObjTest extends HackTest {
       array('toNotContain', dict['x' => 1, 'y' => 2, 'z' => 3], 2),
       array('toContain', dict[], 2),
 
+      array('toContainSubstring', 'foo', 'a'),
+      array('toNotContainSubstring', 'foo', 'o'),
+
       array('toContainKey', dict['x' => 1, 'y' => 2, 'z' => 3], '1'),
       array('toNotContainKey', dict['x' => 1, 'y' => 2, 'z' => 3], 'y'),
       array('toContainKey', dict[], 'a'),