[speech-commands] Fix a flaky test and a wrong console message (#143)

- Fixes tensorflow/tfjs#1192
  The previous assumption was that the kernel of the dense
  layer gets updated. But sometimes, the bias updates and
  the kernel doesn't.
- A console.log message regarding large datasets and the use
  of fitDataset() was placed in the wrong place. This PR fixes
  that as well.

Author: caisq

speech-commands/src/browser_fft_recognizer.ts

@@ -917,12 +917,12 @@ class TransferBrowserFftSpeechCommandRecognizer extends
     const datasetDurationMillisThreshold =
         config.fitDatasetDurationMillisThreshold == null ?
         60e3 : config.fitDatasetDurationMillisThreshold;
-    console.log(
-        `Detected large dataset: total duration = ` +
-        `${this.dataset.durationMillis()} ms > ` +
-        `${datasetDurationMillisThreshold} ms. ` +
-        `Training transfer model using fitDataset() instead of fit()`);
     if (this.dataset.durationMillis() > datasetDurationMillisThreshold) {
+      console.log(
+          `Detected large dataset: total duration = ` +
+          `${this.dataset.durationMillis()} ms > ` +
+          `${datasetDurationMillisThreshold} ms. ` +
+          `Training transfer model using fitDataset() instead of fit()`);
       return await this.trainOnDataset(config);
     } else {
       return await this.trainOnTensors(config);

speech-commands/src/browser_fft_recognizer_test.ts

@@ -880,8 +880,9 @@ describeWithFlags('Browser FFT recognizer', tf.test_util.NODE_ENVS, () => {
     // tslint:disable-next-line:no-any
     const transferHead = (transfer as any).transferHead as tf.Sequential;
     const numLayers = transferHead.layers.length;
-    const oldTransferKernel =
-        transferHead.getLayer(null, numLayers - 1).getWeights()[0].dataSync();
+    const oldTransferWeightValues =
+        transferHead.getLayer(null, numLayers - 1).getWeights()
+        .map(weight => weight.dataSync());
 
     const history =
         await transfer.train({optimizer: tf.train.sgd(1)}) as tf.History;
@@ -897,19 +898,21 @@ describeWithFlags('Browser FFT recognizer', tf.test_util.NODE_ENVS, () => {
 
     // Verify that the weights of the dense layer in the base model doesn't
     // change, i.e., is frozen.
-    const newTransferKernel =
-        transferHead.getLayer(null, numLayers - 1).getWeights()[0].dataSync();
+    const newTransferWeightValues =
+        transferHead.getLayer(null, numLayers - 1).getWeights()
+        .map(weight => weight.dataSync());
     baseModelOldWeightValues.forEach((oldWeight, i) => {
       tf.test_util.expectArraysClose(baseModelNewWeightValues[i], oldWeight);
     });
     // Verify that the weight of the transfer-learning head model changes
     // after training.
-    expect(tf.tensor1d(newTransferKernel)
-               .sub(tf.tensor1d(oldTransferKernel))
-               .abs()
-               .max()
-               .dataSync()[0])
-        .toBeGreaterThan(1e-3);
+    const maxWeightChanges = newTransferWeightValues.map(
+        (newValues, i) => tf.tensor1d(newValues)
+            .sub(tf.tensor1d(oldTransferWeightValues[i]))
+            .abs()
+            .max()
+            .dataSync()[0]);
+    expect(Math.max(...maxWeightChanges)).toBeGreaterThan(1e-3);
 
     // Test recognize() with the transfer recognizer.
     const spectrogram =