Fix isValidSHA1

Lint fix broke isValidSHA1.  Use RegExp.test rather than
string.match.  Anchor regular expression.  Add tests.

[changelog:fixed]

lib/common/git/handlePushBasedEventOnRepo.ts

@@ -69,7 +69,7 @@ function validateEventOnRepo(payload: EventOnRepo): boolean {
 }
 
 export function isValidSHA1(s: string): boolean {
-    return s.match(/[a-fA-F0-9]{40}/) !== undefined;
+    return /^[a-fA-F0-9]{40}$/.test(s);
 }
 
 /**

test/common/git/handlePushBasedEventOnRepo.test.ts

@@ -0,0 +1,51 @@
+/*
+ * Copyright © 2019 Atomist, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as assert from "power-assert";
+import { isValidSHA1 } from "../../../lib/common/git/handlePushBasedEventOnRepo";
+
+describe("common/git/handlePushBasedEventOnRepo", () => {
+
+    describe("isValidSHA1", () => {
+
+        it("should validate a SHA1", () => {
+            const ss = [
+                "1234567890abcdef1234567890abcdef12345678",
+                "33e38b6c72788866004acfd736ed12b2e9529ea7",
+                "f6dee8b272248aab385f840f4799a707dcb7af26",
+                "b8947fc4370c99d3137d7d6b6e20ec26c8036370",
+            ];
+            ss.forEach(s => assert(isValidSHA1(s)));
+        });
+
+        it("should not validate invalid SHA1", () => {
+            const ss = [
+                // tslint:disable-next-line:no-null-keyword
+                null,
+                undefined,
+                "",
+                "master",
+                "some-branch",
+                "other/branch",
+                "b8947fc4370c99d3137d7d6b6e20ec26c8036370a",
+                "masterb8947fc4370c99d3137d7d6b6e20ec26c8036370",
+            ];
+            ss.forEach(s => assert(!isValidSHA1(s)));
+        });
+
+    });
+
+});