Moved willUpdate logic into it's own function

- This logic is clogging up the getConfig function, making it harder
  to reason about what getConfig is doing
- I have a hunch we don't need getConfig at all...
- This is a step in a hopefully better direction

Author: ErisDS

packages/jest-snapshot/lib/SnapshotManager.js

@@ -14,6 +14,21 @@ class SnapshotManager {
         this.defaultSnapshotRoot = '__snapshots__';
     }
 
+    /**
+     * Determines whether to update all snapshots or only new ones
+     * @returns {string} e.g. 'all' or 'new'
+     */
+    _willUpdate() {
+        const updateSnapshots = (
+            process.env.SNAPSHOT_UPDATE
+            || process.env.UPDATE_SNAPSHOT
+            || process.env.SNAPSHOTS_UPDATE
+            || process.env.UPDATE_SNAPSHOTS
+        );
+
+        return updateSnapshots ? 'all' : 'new';
+    }
+
     /**
      * Looks in the registry for a snapshot with the same filename and nameTemplate
      * If needed, increments the counter
@@ -64,13 +79,7 @@ class SnapshotManager {
         const {testPath, testTitle} = this.currentTest;
 
         const snapshotName = this._getNameForSnapshot(testPath, testTitle);
-        const updateSnapshots = (
-            process.env.SNAPSHOT_UPDATE
-            || process.env.UPDATE_SNAPSHOT
-            || process.env.SNAPSHOTS_UPDATE
-            || process.env.UPDATE_SNAPSHOTS
-        );
-        const willUpdate = updateSnapshots ? 'all' : 'new';
+        const willUpdate = this._willUpdate();
 
         // Set full path
         const snapshotPath = this._resolveSnapshotFilePath(testPath);

packages/jest-snapshot/test/SnapshotManager.test.js

@@ -117,6 +117,22 @@ describe('Snapshot Manager', function () {
         assert.equal(result, '/abc/cde/__snapshots__/a.test.js.snap');
     });
 
+    it('_willUpdate: will return all when the environment variable is set', function () {
+        const originalValue = process.env.SNAPSHOT_UPDATE || '';
+        process.env.SNAPSHOT_UPDATE = 1;
+        const snapshotManager = new SnapshotManager();
+        assert.equal(snapshotManager._willUpdate(), 'all');
+        process.env.SNAPSHOT_UPDATE = originalValue;
+    });
+
+    it('_willUpdate: will return new when the environment variable is not set', function () {
+        const originalValue = process.env.SNAPSHOT_UPDATE || '';
+        process.env.SNAPSHOT_UPDATE = '';
+        const snapshotManager = new SnapshotManager();
+        assert.equal(snapshotManager._willUpdate(), 'new');
+        process.env.SNAPSHOT_UPDATE = originalValue;
+    });
+
     it('_getConfig: will throw if no current test is set', function () {
         const snapshotManager = new SnapshotManager();