Remove cpu backend in tfjs-node testing, use fake instead.

[lina128]

Node test use cpu backend: https://github.com/tensorflow/tfjs/blob/master/tfjs-node/src/image_test.ts#L224

The test total was 3738, comparing to 3724 after. The 14 tests belong to array_util_test and complex_util_test in backends, which is not backend agnostic and thus excluded from tests.ts. This is expected.

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This change is 

[tafsiri]

@lina128 Is that the only test in node backend that uses CPU?

I think this test should be changed as none of its behaviour depends on the CPU backend specifically. Rather than use the CPU backend it should create a mock backend and set it and run its test.

See engine_test for examples of this. kernel_registry_test also does uses the same approach.

Reviewable status: 0 of 1 approvals obtained (waiting on @kangyizhang, @pyu10055, and @tafsiri)

[lina128]

Good idea. Done.

Reviewable status: 0 of 1 approvals obtained (waiting on @kangyizhang and @pyu10055)

[tafsiri]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @kangyizhang, @lina128, @pyu10055, and @tafsiri)

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tfjs-node/src/image_test.ts, line 227 at r1 (raw file):

    try {
      const testBackend = new TestKernelBackend();
      registerBackend('sync', () => testBackend);

nit: rename this to something else (e.g. 'testBackend'). the sync nature of it isn't particularly relevant here.

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tfjs-node/src/nodejs_kernel_backend_test.ts, line 82 at r1 (raw file):

      const testBackend = new TestKernelBackend();
      tf.registerBackend('sync', () => testBackend);
      tf.setBackend('sync');

nit: same as above.

[lina128]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @kangyizhang and @pyu10055)

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tfjs-node/src/image_test.ts, line 227 at r1 (raw file):

Previously, tafsiri (Yannick Assogba) wrote…

nit: rename this to something else (e.g. 'testBackend'). the sync nature of it isn't particularly relevant here.

Done.

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tfjs-node/src/nodejs_kernel_backend_test.ts, line 82 at r1 (raw file):

Previously, tafsiri (Yannick Assogba) wrote…

nit: same as above.

Done.