Make a start on a unit test for megolm alg impl

not much here yet, but it's a start at least.

spec/unit/crypto/algorithms/megolm.spec.js

@@ -0,0 +1,109 @@
+try {
+    global.Olm = require('olm');
+} catch (e) {
+    console.warn("unable to run megolm tests: libolm not available");
+}
+
+import expect from 'expect';
+
+import sdk from '../../../..';
+import algorithms from '../../../../lib/crypto/algorithms';
+import WebStorageSessionStore from '../../../../lib/store/session/webstorage';
+import MockStorageApi from '../../../MockStorageApi';
+import testUtils from '../../../test-utils';
+
+// Crypto and OlmDevice won't import unless we have global.Olm
+let OlmDevice;
+let Crypto;
+if (global.Olm) {
+    OlmDevice = require('../../../../lib/crypto/OlmDevice');
+    Crypto = require('../../../../lib/crypto');
+}
+
+const MatrixEvent = sdk.MatrixEvent;
+const MegolmDecryption = algorithms.DECRYPTION_CLASSES['m.megolm.v1.aes-sha2'];
+
+const ROOM_ID = '!ROOM:ID';
+
+describe("MegolmDecryption", function() {
+    if (!global.Olm) {
+        console.warn('Not running megolm unit tests: libolm not present');
+        return;
+    }
+
+    let megolmDecryption;
+    let mockOlmLib;
+    let mockCrypto;
+    let mockBaseApis;
+
+    beforeEach(function() {
+        testUtils.beforeEach(this); // eslint-disable-line no-invalid-this
+
+        mockCrypto = testUtils.mock(Crypto, 'Crypto');
+        mockBaseApis = {};
+
+        const mockStorage = new MockStorageApi();
+        const sessionStore = new WebStorageSessionStore(mockStorage);
+
+        const olmDevice = new OlmDevice(sessionStore);
+
+        megolmDecryption = new MegolmDecryption({
+            userId: '@user:id',
+            crypto: mockCrypto,
+            olmDevice: olmDevice,
+            baseApis: mockBaseApis,
+            roomId: ROOM_ID,
+        });
+
+
+        // we stub out the olm encryption bits
+        mockOlmLib = {};
+        mockOlmLib.ensureOlmSessionsForDevices = expect.createSpy();
+        mockOlmLib.encryptMessageForDevice = expect.createSpy();
+        megolmDecryption.olmlib = mockOlmLib;
+    });
+
+    describe('receives some keys:', function() {
+        let groupSession;
+        beforeEach(function() {
+            groupSession = new global.Olm.OutboundGroupSession();
+            groupSession.create();
+
+            const event = new MatrixEvent({});
+            event.setClearData(
+                {
+                    type: 'm.room_key',
+                    content: {
+                        algorithm: 'm.megolm.v1.aes-sha2',
+                        room_id: ROOM_ID,
+                        session_id: groupSession.session_id(),
+                        session_key: groupSession.session_key(),
+                    },
+                },
+                "SENDER_CURVE25519",
+                "SENDER_ED25519",
+            );
+
+            megolmDecryption.onRoomKeyEvent(event);
+        });
+
+        it('can decrypt an event', function() {
+            const event = new MatrixEvent({
+                type: 'm.room.encrypted',
+                room_id: ROOM_ID,
+                content: {
+                    algorithm: 'm.megolm.v1.aes-sha2',
+                    sender_key: "SENDER_CURVE25519",
+                    session_id: groupSession.session_id(),
+                    ciphertext: groupSession.encrypt(JSON.stringify({
+                        room_id: ROOM_ID,
+                        content: 'testytest',
+                    })),
+                },
+            });
+
+            megolmDecryption.decryptEvent(event);
+            expect(event.getContent()).toEqual('testytest');
+        });
+    });
+});

src/crypto/algorithms/megolm.js

@@ -520,6 +520,9 @@ function MegolmDecryption(params) {
     // events which we couldn't decrypt due to unknown sessions / indexes: map from
     // senderKey|sessionId to list of MatrixEvents
     this._pendingEvents = {};
+
+    // this gets stubbed out by the unit tests.
+    this.olmlib = olmlib;
 }
 utils.inherits(MegolmDecryption, base.DecryptionAlgorithm);
 
@@ -698,7 +701,7 @@ MegolmDecryption.prototype.shareKeysWithDevice = function(keyRequest) {
     const deviceInfo = this._crypto.getStoredDevice(userId, deviceId);
     const body = keyRequest.requestBody;
 
-    olmlib.ensureOlmSessionsForDevices(
+    this.olmlib.ensureOlmSessionsForDevices(
         this._olmDevice, this._baseApis, {
             [userId]: [deviceInfo],
         },
@@ -741,7 +744,7 @@ MegolmDecryption.prototype.shareKeysWithDevice = function(keyRequest) {
             ciphertext: {},
         };
 
-        olmlib.encryptMessageForDevice(
+        this.olmlib.encryptMessageForDevice(
             encryptedContent.ciphertext,
             this._userId,
             this._deviceId,