diff --git a/packages/common/http/testing/src/backend.ts b/packages/common/http/testing/src/backend.ts
index d5311fd551..75a32389b8 100644
--- a/packages/common/http/testing/src/backend.ts
+++ b/packages/common/http/testing/src/backend.ts
@@ -90,7 +90,19 @@ export class HttpClientTestingBackend implements HttpBackend, HttpTestingControl
           `Expected one matching request for criteria "${description}", found ${matches.length} requests.`);
     }
     if (matches.length === 0) {
-      throw new Error(`Expected one matching request for criteria "${description}", found none.`);
+      let message = `Expected one matching request for criteria "${description}", found none.`;
+      if (this.open.length > 0) {
+        // Show the methods and URLs of open requests in the error, for convenience.
+        const requests = this.open
+                             .map(testReq => {
+                               const url = testReq.request.urlWithParams;
+                               const method = testReq.request.method;
+                               return `${method} ${url}`;
+                             })
+                             .join(', ');
+        message += ` Requests received are: ${requests}.`;
+      }
+      throw new Error(message);
     }
     return matches[0];
   }
diff --git a/packages/common/http/testing/test/request_spec.ts b/packages/common/http/testing/test/request_spec.ts
index aefb5d0a4e..2b03893447 100644
--- a/packages/common/http/testing/test/request_spec.ts
+++ b/packages/common/http/testing/test/request_spec.ts
@@ -36,7 +36,9 @@ describe('HttpClient TestRequest', () => {
       fail();
     } catch (error) {
       expect(error.message)
-          .toBe('Expected one matching request for criteria "Match URL: /some-url", found none.');
+          .toBe(
+              'Expected one matching request for criteria "Match URL: /some-url", found none.' +
+              ' Requests received are: GET /some-other-url.');
     }
   });
 
@@ -55,7 +57,8 @@ describe('HttpClient TestRequest', () => {
     } catch (error) {
       expect(error.message)
           .toBe(
-              'Expected one matching request for criteria "Match URL: /some-url?query=world", found none.');
+              'Expected one matching request for criteria "Match URL: /some-url?query=world", found none.' +
+              ' Requests received are: GET /some-url?query=hello.');
     }
   });
 });