fix streaming packing test (#2454)

* fix streaming packing test

* constrain amount of text generated

tests/test_packed_pretraining.py

@@ -23,22 +23,26 @@ class TestPretrainingPacking:
         # seed with random.seed(0) for reproducibility
         random.seed(0)
 
-        # generate 20 rows of random text with "words" of between 2 and 10 characters and
+        # generate row of random text with "words" of between 2 and 10 characters and
         # between 400 to 1200 characters per line
-        data = [
-            "".join(random.choices(string.ascii_lowercase, k=random.randint(2, 10)))
-            for _ in range(20)
-        ] + [
-            " ".join(
-                random.choices(string.ascii_lowercase, k=random.randint(400, 1200))
+        def rand_txt():
+            return " ".join(
+                [
+                    "".join(
+                        random.choices(string.ascii_lowercase, k=random.randint(2, 10))
+                    )
+                    for _ in range(random.randint(50, 200))
+                ]
             )
-            for _ in range(20)
-        ]
+
+        # Create a list of 2000 random texts rather than just using it within the
+        # generator so the test runs faster
+        data = [rand_txt() for _ in range(500)]
 
         # Create an IterableDataset
         def generator():
-            for text in data:
-                yield {"text": text}
+            for row in data:
+                yield {"text": row}
 
         return IterableDataset.from_generator(generator)
 
@@ -92,7 +96,7 @@ class TestPretrainingPacking:
         )
         idx = 0
         for data in trainer_loader:
-            if idx > 10:
+            if idx > 3:
                 break
             assert data["input_ids"].shape == torch.Size(
                 [1, original_bsz * cfg.sequence_len]