diff --git a/src/ExpectObj.hack b/src/ExpectObj.hack
index dd29b3f..4d9f743 100644
--- a/src/ExpectObj.hack
+++ b/src/ExpectObj.hack
@@ -227,30 +227,39 @@ class ExpectObj<T> extends Assert {
   }
 
   /**
-   * Assert: For strings, Str\contains($actual, $needle) !== false
-   *         For containers (array, Map, Set, etc) or objects which implement
-   *         Traversable, iterate through $actual and see if any element ==
-   *         $needle.
+   * Assert: iterate through $actual and see if any element == $needle.
    * Note:   If $needle is an object, === will be used.
    */
-  public function toContain(
-    mixed $needle,
+  public function toContain<TVal>(
+    TVal $needle,
     string $msg = '',
     mixed ...$args
-  ): void {
+  ): void where T as Traversable<TVal>{
     $msg = \vsprintf($msg, $args);
     $this->assertContains($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.
    */
-  public function toContainKey(
-    mixed $key,
+  public function toContainKey<TKey as arraykey, TVal>(
+    TKey $key,
     string $msg = '',
     mixed ...$args
-  ): void {
+  ): void where T as KeyedContainer<TKey, TVal> {
     $msg = \vsprintf($msg, $args);
     $obj = $this->var;
     invariant(
@@ -441,13 +450,19 @@ class ExpectObj<T> extends Assert {
   }
 
   /**
-   * Assert: For strings, Str\contains($actual, $needle) !== false
-   *         For containers (array, Map, Set, etc) or objects which implement
-   *         Traversable, iterate through $actual and make sure there is no
+   * Assert: iterate through $actual and make sure there is no
    *         element for which $element == $needle.
    * Note:   If $needle is an object, === will be used.
    */
-  public function toNotContain(mixed $expected, string $msg = '', mixed ...$args): void {
+  public function toNotContain<TVal>(TVal $expected, string $msg = '', mixed ...$args): void where T as Traversable<TVal> {
+    $msg = \vsprintf($msg, $args);
+    $this->assertNotContains($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);
   }
@@ -456,7 +471,7 @@ class ExpectObj<T> extends Assert {
    * Assert: That the KeyedTraversible $key has a key set.
    * Note:   If $key is a Set, use assertContains.
    */
-  public function toNotContainKey(arraykey $key, string $msg = '', mixed ...$args): void where T as KeyedContainer<arraykey, mixed> {
+  public function toNotContainKey<TKey as arraykey, TVal>(TKey $key, string $msg = '', mixed ...$args): void where T as KeyedContainer<TKey, TVal> {
     $msg = \vsprintf($msg, $args);
     $obj = $this->var;
     $this->assertFalse(\array_key_exists($key, $obj), $msg);
@@ -524,51 +539,32 @@ class ExpectObj<T> extends Assert {
    *
    *   expect(function() { invariant_violation('fail'); })
    *     ->toThrow(InvariantViolationException::class, 'fail');
+   *
+   * If `TRet` is an `Awaitable<_>` (e.g. if an async function is provided),
+   * the awaitable will be awaited.
    */
-  public function toThrow<Tclass as \Exception>(
-    classname<Tclass> $exception_class,
+  public function toThrow<TException as \Throwable, TRet>(
+    classname<TException> $exception_class,
     ?string $expected_exception_message = null,
     ?string $msg = null,
     mixed ...$args
-  ): void {
-    $msg = \vsprintf($msg, $args);
-    $this->toThrowWhenCalledWith(
-      varray[],
-      $exception_class,
-      $expected_exception_message,
-      $msg,
-    );
-  }
-
-  /**
-   * Asserts: Function throws exception of given type and with the given
-   *          exception message (optional)
-   *
-   * Example usage:
-   *
-   *   expect(
-   *     function($a) { if ($a == 'foo') { invariant_violation('fail'); }}
-   *   )->toThrowWhenCalledWith(array('foo'), 'InvariantViolationException');
-   */
-  public function toThrowWhenCalledWith<Tclass as \Exception>(
-    Container<mixed> $args,
-    classname<Tclass> $exception_class,
-    ?string $expected_exception_message = null,
-    ?string $desc = null,
-  ): void {
-    $exception = $this->tryCallWithArgsReturnException($args, $exception_class);
+  ): TException where T = (function(): TRet) {
+    $msg = \vsprintf($msg ?? '', $args);
+    $exception = $this->tryCallWithArgsReturnException(vec[], $exception_class);
 
     if (!$exception) {
       throw new \Exception(
-        $desc.": Expected exception ".$exception_class." wasn't thrown",
+        $msg.": Expected exception ".$exception_class." wasn't thrown",
       );
     }
 
     if ($expected_exception_message !== null) {
       $message = $exception->getMessage();
 
-      $this->assertContains($expected_exception_message, $message, $desc ?? '');
+      $this->assertContains($expected_exception_message, $message, $msg);
     }
+
+    return $exception;
   }
 
   /***************************************
@@ -576,7 +572,7 @@ class ExpectObj<T> extends Assert {
    **** Private implementation details ***
    ***************************************
    ***************************************/
-  private function tryCallWithArgsReturnException<Tclass as \Exception>(
+  private function tryCallWithArgsReturnException<Tclass as \Throwable>(
     Container<mixed> $args,
     classname<Tclass> $expected_exception_type,
   ): ?Tclass {
diff --git a/tests/ExpectObjTest.hack b/tests/ExpectObjTest.hack
index 1c8fc9b..d7fbb51 100644
--- a/tests/ExpectObjTest.hack
+++ b/tests/ExpectObjTest.hack
@@ -57,6 +57,9 @@ final class ExpectObjTest extends HackTest {
     expect(dict[])->toBeType('KeyedContainer');
     expect(varray[1, 2, 3])->toContain(2);
     expect(varray[1, 2, 3])->toNotContain(7);
+    expect('foo')->toContainSubstring('foo');
+    expect('foo')->toContainSubstring('o');
+    expect('foo')->toNotContainSubstring('a');
     expect(1)->toAlmostEqual(1);
     expect(null)->toAlmostEqual(null);
 
@@ -241,31 +244,6 @@ final class ExpectObjTest extends HackTest {
   //
   // Tests for toThrow methods
   //
-  public function testToThrowWhenCalledWithSuccess(): void {
-    expect(
-      function() {
-        throw new \Exception();
-      },
-    )->toThrow(\Exception::class);
-
-    expect(
-      (classname<\Exception> $class) ==> {
-        if ($class === ExpectObjTestException::class) {
-          throw new ExpectObjTestException();
-        }
-      },
-    )->toThrowWhenCalledWith(
-      varray[ExpectObjTestException::class],
-      ExpectObjTestException::class,
-    );
-
-    expect(
-      function() {
-        throw new ExpectObjTestException('test msg');
-      },
-    )->toThrow(ExpectObjTestException::class, 'test msg');
-  }
-
   public function testToThrowWithMessage(): void {
     expect(
       function() {
@@ -291,16 +269,14 @@ final class ExpectObjTest extends HackTest {
 
   public function testAwaitableFunctionGetsPrepped(): void {
     expect(
-      async (mixed $class) ==> {
+      async () ==> {
+        $class = ExpectObjTestException::class;
         await self::stopEagerExecution();
         if ($class === ExpectObjTestException::class) {
           throw new ExpectObjTestException();
         }
       },
-    )->toThrowWhenCalledWith(
-      varray[ExpectObjTestException::class],
-      ExpectObjTestException::class,
-    );
+    )->toThrow(ExpectObjTestException::class);
   }
 
   public function testToHaveSameShapeAsSuccess(): void {
@@ -466,9 +442,14 @@ final class ExpectObjTest extends HackTest {
     try {
       expect("a\nb\nd\n")->toBeSame("a\nb\nc\n");
     } catch (ExpectationFailedException $e) {
-      expect($e->getMessage())->toContain(" a\n b\n-c\n+d\n");
+      expect($e->getMessage())->toContainSubstring(" a\n b\n-c\n+d\n");
       return;
     }
     self::fail("Should have thrown an exception");
   }
+
+  public function testToThrowReturnsException(): void {
+    $e = expect(() ==> { throw new \Exception("Hello, world"); })->toThrow(\Exception::class);
+    expect($e->getMessage())->toContainSubstring('Hello, world');
+  }
 }