add multi device test

Author: jshin1394

src/metrax/metrics_test.py

@@ -16,10 +16,12 @@
 
 from absl.testing import absltest
 from absl.testing import parameterized
+import jax
 import jax.numpy as jnp
 import keras_hub
 import metrax
 import numpy as np
+import os
 from sklearn import metrics as sklearn_metrics
 
 np.random.seed(42)
@@ -172,6 +174,40 @@ def test_perplexity_empty(self):
     self.assertEqual(m.aggregate_crossentropy, jnp.array(0, jnp.float32))
     self.assertEqual(m.num_samples, jnp.array(0, jnp.float32))
 
+  def test_multiple_devices(self):
+    """Test that metrax metrics work across multiple devices using R2 as an example."""
+
+    def create_r2(logits, labels):
+      """Creates a metrax R2 metric given logits and labels."""
+      return metrax.RSQUARED.from_model_output(logits, labels)
+
+    def sharded_r2(logits, labels):
+      """Calculates sharded MSE across devices."""
+      num_devices = jax.device_count()
+
+      shard_size = logits.shape[0] // num_devices
+      sharded_logits = logits.reshape(num_devices, shard_size, logits.shape[-1])
+      sharded_labels = labels.reshape(num_devices, shard_size, labels.shape[-1])
+
+      r2_for_devices = jax.pmap(create_r2)(sharded_logits, sharded_labels)
+      return r2_for_devices
+
+    y_pred = OUTPUT_PREDS
+    y_true = OUTPUT_LABELS
+    metric = jax.jit(sharded_r2)(y_pred, y_true)
+    metric = metric.reduce()
+
+    expected = sklearn_metrics.r2_score(
+        y_true.flatten(),
+        y_pred.flatten(),
+    )
+    np.testing.assert_allclose(
+        metric.compute(),
+        expected,
+        rtol=1e-05,
+        atol=1e-05,
+    )
+
   @parameterized.named_parameters(
       ('basic', OUTPUT_LABELS, OUTPUT_PREDS, 0.5),
       ('high_threshold', OUTPUT_LABELS, OUTPUT_PREDS, 0.7),
@@ -415,4 +451,7 @@ def test_perplexity(self, y_true, y_pred, sample_weights):
 
 
 if __name__ == '__main__':
+  os.environ['XLA_FLAGS'] = (
+      '--xla_force_host_platform_device_count=4'  # Use 4 CPU devices
+  )
   absltest.main()