part: Fix the insertion&watches test case

Prefix search uses the watch channels of inner nodes rather than the
leaves since the leaf channel only closes when the leaf itself is
mutated (but not when it's moved). Change the test case to match with
the implementation.

Signed-off-by: Jussi Maki <[email protected]>

part/part_test.go

@@ -65,14 +65,18 @@ func Test_insertion_and_watches(t *testing.T) {
 		assertClosed(t, w2)
 
 		assertOpen(t, w3)
-		assertOpen(t, w4)
+
+		// Prefix watch is closed as it's on the "ab" node
+		// since that's the closest non-leaf node to "abc" leaf.
+		assertClosed(t, w4)
 	}
 
 	// Root to leaf and back.
-	// N4() -- Insert(a, 1) -> L(a, 1) -- Insert(b, 2) -> N4()
-	//                                                   /   \
-	//                                             L(a, 1)    L(b, 2)
-	// Neither the Get(a) nor the Prefix(a) watch channels should close.
+	// N4() -- Insert(a, 1) -> N4() -- Insert(b, 2) -> N4()
+	//                         /                      /   \
+	//                      L(a, 1)             L(a, 1)    L(b, 2)
+	// The Get(a) channel closes, but not Prefix(a) since the prefix search
+	// uses the root channel.
 	{
 		tree := New[int]()
 
@@ -86,7 +90,7 @@ func Test_insertion_and_watches(t *testing.T) {
 
 		_, _, tree = tree.Insert([]byte("b"), 2)
 		assertOpen(t, w)
-		assertOpen(t, w2)
+		assertClosed(t, w2)
 	}
 
 	// "Lateral movement" - L(a, 1) should become the leaf of the root N4