chore: improve test coverage

Author: jeswr

asynciterator.ts

@@ -1753,9 +1753,11 @@ export class UnionIterator<T> extends AsyncIterator<T> {
     while (this._size < this._maxParallelIterators && (iterator = _sources.read()) !== null) {
       // TODO - it would be nice to skip adding sources if it is a single or no
       // element iterator.
-      this._addSource(iterator);
-      if ((item = iterator.read()) !== null)
-        return item;
+      // if (!iterator.done) {
+        this._addSource(iterator);
+        if ((item = iterator.read()) !== null)
+          return item;
+      // }
     }
 
     if (this._size === 0 && this._sources.done)
@@ -1798,7 +1800,10 @@ function destinationRemoveEmptySources<T>(this: InternalSource<T>) {
 
     // else if (destination._size < destination._maxParallelIterators && destination._sources.readable) {
     // TODO: Add a test case for this
-    this.readable = true;
+    if (this.readable)
+      this.emit('readable')
+    else
+      this.readable = true;
     // TODO: Future performance improvement - continue re-filling the circular linked list
     // }
   }

test/UnionIterator-test.js

@@ -68,6 +68,27 @@ describe('UnionIterator', () => {
     (await toArray(iterator)).sort().should.eql([0, 1, 2]);
   });
 
+  it('should include all data from 0 sources - with maxParallelIterators: 1', async () => {
+    const iterator = new UnionIterator([
+    ], { maxParallelIterators: 1 });
+    (await toArray(iterator)).sort().should.eql([]);
+  });
+
+  it('should include all data from 1 non-empty source - with maxParallelIterators: 1', async () => {
+    const iterator = new UnionIterator([
+      range(0, 2),
+    ], { maxParallelIterators: 1 });
+    (await toArray(iterator)).sort().should.eql([0, 1, 2]);
+  });
+
+  it('should include all data from 2 non-empty sources - with maxParallelIterators: 1', async () => {
+    const iterator = new UnionIterator([
+      range(0, 2),
+      range(3, 4),
+    ], { maxParallelIterators: 1 });
+    (await toArray(iterator)).sort().should.eql([0, 1, 2, 3, 4]);
+  });
+
   it('should include all data from 1 non-empty and 4 empty sources - with maxParallelIterators: 1', async () => {
     const iterator = new UnionIterator([
       new EmptyIterator(),
@@ -79,6 +100,23 @@ describe('UnionIterator', () => {
     (await toArray(iterator)).sort().should.eql([0, 1, 2]);
   });
 
+  it('should include all data from 4 empty sources - with maxParallelIterators: 1', async () => {
+    const iterator = new UnionIterator([
+      new EmptyIterator(),
+      new EmptyIterator(),
+      new EmptyIterator(),
+      new EmptyIterator(),
+    ], { maxParallelIterators: 1 });
+    (await toArray(iterator)).sort().should.eql([]);
+  });
+
+  it('should include all data from 1 empty source - with maxParallelIterators: 1', async () => {
+    const iterator = new UnionIterator([
+      new EmptyIterator(),
+    ], { maxParallelIterators: 1 });
+    (await toArray(iterator)).sort().should.eql([]);
+  });
+
   describe('when constructed with an array of 0 sources', () => {
     let iterator;
     before(() => {