improved error msg on toBeRehectedWithError and all other built-in async matchers

spec/core/matchers/async/toBePendingSpec.js

@@ -38,6 +38,8 @@ describe('toBePending', function() {
       return matcher.compare(actual);
     }
 
-    expect(f).toThrowError('Expected toBePending to be called on a promise.');
+    expect(f).toThrowError(
+      `Expected toBePending to be called on a promise but was on a ${typeof actual}.`
+    );
   });
 });

spec/core/matchers/async/toBeRejectedSpec.js

@@ -28,6 +28,8 @@ describe('toBeRejected', function() {
       return matcher.compare(actual);
     }
 
-    expect(f).toThrowError('Expected toBeRejected to be called on a promise.');
+    expect(f).toThrowError(
+      `Expected toBeRejected to be called on a promise but was on a ${typeof actual}.`
+    );
   });
 });

spec/core/matchers/async/toBeRejectedWithErrorSpec.js

@@ -232,7 +232,7 @@ describe('#toBeRejectedWithError', function() {
     }
 
     expect(f).toThrowError(
-      'Expected toBeRejectedWithError to be called on a promise.'
+      `Expected toBeRejectedWithError to be called on a promise but was on a ${typeof actual}.`
     );
   });
 });

spec/core/matchers/async/toBeRejectedWithSpec.js

@@ -83,7 +83,7 @@ describe('#toBeRejectedWith', function() {
     }
 
     expect(f).toThrowError(
-      'Expected toBeRejectedWith to be called on a promise.'
+      `Expected toBeRejectedWith to be called on a promise but was on a ${typeof actual}.`
     );
   });
 });

spec/core/matchers/async/toBeResolvedSpec.js

@@ -35,6 +35,8 @@ describe('toBeResolved', function() {
       return matcher.compare(actual);
     }
 
-    expect(f).toThrowError('Expected toBeResolved to be called on a promise.');
+    expect(f).toThrowError(
+      `Expected toBeResolved to be called on a promise but was on a ${typeof actual}.`
+    );
   });
 });

spec/core/matchers/async/toBeResolvedToSpec.js

@@ -93,7 +93,7 @@ describe('#toBeResolvedTo', function() {
     }
 
     expect(f).toThrowError(
-      'Expected toBeResolvedTo to be called on a promise.'
+      `Expected toBeResolvedTo to be called on a promise but was on a ${typeof actual}.`
     );
   });
 });