e2e: tweak semantics of waitForHeight (#6943)

light/client.go

@@ -379,6 +379,7 @@ func (c *Client) Update(ctx context.Context, now time.Time) (*types.LightBlock,
 		return nil, err
 	}
 
+	// If there is a new light block then verify it
 	if latestBlock.Height > lastTrustedHeight {
 		err = c.verifyLightBlock(ctx, latestBlock, now)
 		if err != nil {
@@ -388,7 +389,8 @@ func (c *Client) Update(ctx context.Context, now time.Time) (*types.LightBlock,
 		return latestBlock, nil
 	}
 
-	return nil, nil
+	// else return the latestTrustedBlock
+	return c.latestTrustedBlock, nil
 }
 
 // VerifyLightBlockAtHeight fetches the light block at the given height

light/client_test.go

@@ -644,7 +644,7 @@ func TestClientReplacesPrimaryWithWitnessIfPrimaryIsUnavailable(t *testing.T) {
 		chainID,
 		trustOptions,
 		mockDeadNode,
-		[]provider.Provider{mockFullNode, mockFullNode},
+		[]provider.Provider{mockDeadNode, mockFullNode},
 		dbs.New(dbm.NewMemDB()),
 		light.Logger(log.TestingLogger()),
 	)
@@ -663,6 +663,32 @@ func TestClientReplacesPrimaryWithWitnessIfPrimaryIsUnavailable(t *testing.T) {
 	mockFullNode.AssertExpectations(t)
 }
 
+func TestClientReplacesPrimaryWithWitnessIfPrimaryDoesntHaveBlock(t *testing.T) {
+	mockFullNode := &provider_mocks.Provider{}
+	mockFullNode.On("LightBlock", mock.Anything, mock.Anything).Return(l1, nil)
+
+	mockDeadNode := &provider_mocks.Provider{}
+	mockDeadNode.On("LightBlock", mock.Anything, mock.Anything).Return(nil, provider.ErrLightBlockNotFound)
+	c, err := light.NewClient(
+		ctx,
+		chainID,
+		trustOptions,
+		mockDeadNode,
+		[]provider.Provider{mockDeadNode, mockFullNode},
+		dbs.New(dbm.NewMemDB()),
+		light.Logger(log.TestingLogger()),
+	)
+	require.NoError(t, err)
+	_, err = c.Update(ctx, bTime.Add(2*time.Hour))
+	require.NoError(t, err)
+
+	// we should still have the dead node as a witness because it
+	// hasn't repeatedly been unresponsive yet
+	assert.Equal(t, 2, len(c.Witnesses()))
+	mockDeadNode.AssertExpectations(t)
+	mockFullNode.AssertExpectations(t)
+}
+
 func TestClient_BackwardsVerification(t *testing.T) {
 	{
 		headers, vals, _ := genLightBlocksWithKeys(chainID, 9, 3, 0, bTime)