diff --git a/djx/src/test/ts/observable-tests.ts b/djx/src/test/ts/observable-tests.ts
--- a/djx/src/test/ts/observable-tests.ts
+++ b/djx/src/test/ts/observable-tests.ts
@@ -144,30 +144,48 @@ tap.test("of(...) tests", async t => {
         "of(...) should terminate with error when a parameter is rejected"
     );
 
-    t.same(await of(1,2,3).collect(), [1,2,3], ".collect() should return the collected sequence");
-    await t.rejects(of(1,2,3).collect(cancelled), ".collect() should support cancellation");
+    t.same(await of(1, 2, 3).collect(), [1, 2, 3], ".collect() should return the collected sequence");
+    await t.rejects(of(1, 2, 3).collect(cancelled), ".collect() should support cancellation");
 
 }).catch(() => { });
 
 tap.test(".tap() tests", async t => {
     const side: number[] = [];
 
-    of(1,2)
-        .tap({next: v => side.push(v), complete: () => side.push(0)})
-        .tap({next: v => side.push(v*v)})
+    of(1, 2)
+        .tap({ next: v => side.push(v), complete: () => side.push(0) })
+        .tap({ next: v => side.push(v * v) })
         .subscribe({});
 
-    t.same(side, [1,1,2,4,0], ".tap() should be called in the order of registration");
+    t.same(side, [1, 1, 2, 4, 0], ".tap() should be called in the order of registration");
 
     side.length = 0;
 
     await new Promise<void>(resolve => {
-        of(1,2,delay(1).then(() => 3))
-            .tap({next: v => side.push(v)})
-            .tap({ next: v => v === 1 && resolve()})
+        of(1, 2, delay(1).then(() => 3))
+            .tap({ next: v => side.push(v) })
+            .tap({ next: v => v === 1 && resolve() })
             .subscribe({});
     });
 
-    t.same(side, [1,2], ".tap() should be processed synchronously");
+    t.same(side, [1, 2], ".tap() should be processed synchronously");
+
+}).catch(() => { });
+
+tap.test(".while() tests", async t => {
+
+    const seq = of(1, 2, 3, 4).while(v => v <= 2);
+
+    t.same(await seq.collect(), [1, 2], "Should collect only taken elements");
 
-}).catch(() => {});
\ No newline at end of file
+    const data: number[] = [];
+    let complete = 0;
+    seq.subscribe({
+        next: v => data.push(v),
+        complete: () => complete++
+    });
+
+    t.same(data, [1, 2], "Should receive only taken elements");
+    t.equal(complete, 1, "Complete should run once");
+
+}).catch(() => { });
\ No newline at end of file