diff --git a/tests/test_stream.cpp b/tests/test_stream.cpp
--- a/tests/test_stream.cpp
+++ b/tests/test_stream.cpp
@@ -48,7 +48,50 @@ TEST_CASE("construction of stream with p
     }
 }
 
-TEST_CASE("adding data to a stream with no X", "[memory, stream, data]")
+TEST_CASE("changing stream number of channels via sink", "[memory, stream, sink]")
+{
+    Stream s;
+    TestSource so(3, false);
+    so.connect(&s);
+
+    // nc=3, x= false
+    REQUIRE(s.numChannels() == 3);
+    REQUIRE(!s.hasX());
+    for (unsigned i = 0; i < 3; i++)
+    {
+        const StreamChannel* c = s.channel(i);
+        REQUIRE(c != NULL);
+        REQUIRE(c->index() == i);
+    }
+
+    // increase nc value, add X
+    so._setNumChannels(5, true);
+
+    REQUIRE(s.numChannels() == 5);
+    REQUIRE(s.hasX());
+
+    for (unsigned i = 0; i < 5; i++)
+    {
+        const StreamChannel* c = s.channel(i);
+        REQUIRE(c != NULL);
+        REQUIRE(c->index() == i);
+    }
+
+    // reduce nc value, remove X
+    so._setNumChannels(1, false);
+
+    REQUIRE(s.numChannels() == 1);
+    REQUIRE(!s.hasX());
+
+    for (unsigned i = 0; i < 1; i++)
+    {
+        const StreamChannel* c = s.channel(i);
+        REQUIRE(c != NULL);
+        REQUIRE(c->index() == i);
+    }
+}
+
+TEST_CASE("adding data to a stream with no X", "[memory, stream, data, sink]")
 {
     Stream s(3, false, 10);
 
@@ -83,3 +126,55 @@ TEST_CASE("adding data to a stream with 
         }
     }
 }
+
+TEST_CASE("adding data to a stream with X", "[memory, stream, data, sink]")
+{
+    Stream s(3, true, 10);
+
+    // prepare data
+    SamplePack pack(5, 3, true);
+    for (unsigned ci = 0; ci < 3; ci++)
+    {
+        for (unsigned i = 0; i < 5; i++)
+        {
+            pack.data(ci)[i] = i;
+        }
+    }
+    // x data
+    for (unsigned i = 0; i < 5; i++)
+    {
+        pack.xData()[i] = i+10;
+    }
+
+    TestSource so(3, true);
+    so.connect(&s);
+
+    // test
+    so._feed(pack);
+
+    for (unsigned ci = 0; ci < 3; ci++)
+    {
+        const StreamChannel* c = s.channel(ci);
+        const FrameBuffer* y = c->yData();
+
+        for (unsigned i = 0; i < 5; i++)
+        {
+            REQUIRE(y->sample(i) == 0);
+        }
+        for (unsigned i = 5; i < 10; i++)
+        {
+            REQUIRE(y->sample(i) == i-5);
+        }
+    }
+
+    // check x
+    const FrameBuffer* x = s.channel(0)->xData();
+    for (unsigned i = 0; i < 5; i++)
+    {
+        REQUIRE(x->sample(i) == 0);
+    }
+    for (unsigned i = 5; i < 10; i++)
+    {
+        REQUIRE(x->sample(i) == (i-5)+10);
+    }
+}