Add Waveforms for Testing Purposes section to test/README.md (#759)

* add Waveforms for Testing Purposes section

* Update test/README.md

use wrapper function for scipy.io.wavfile.read

Co-authored-by: moto <[email protected]>

* remove un-used files from the doc

* Update test/README.md

Rename variable

Co-authored-by: moto <[email protected]>

* fix indent; remove mentions of unused files

* remove whitenoise* files from README.md

Co-authored-by: moto <[email protected]>

Author: Artyom Astafurov

test/README.md

@@ -41,6 +41,58 @@ The following test modules are defined for corresponding `torchaudio` module/fun
 - [assets/kaldi](./assets/kaldi): Contains Kaldi format matrix files used in [./test_compliance_kaldi.py](./test_compliance_kaldi.py).
 - [compliance](./compliance): Scripts used to generate above Kaldi matrix files.
 
+### Waveforms for Testing Purposes
+
+When testing transforms we often need waveforms of specific type (ex: pure tone, noise, or voice), with specific bitrate (ex. 8 or 16 kHz) and number of channels (ex. mono, stereo). Below are some tips on how to construct waveforms and guidance around existing audio files.
+
+#### Load a Waveform from a File
+
+```python
+filepath = common_utils.get_asset_path('filename.wav')
+waveform, sample_rate = common_utils.load_wav(filepath)
+```
+
+*Note: Should you choose to contribute an audio file, please leave a comment in the issue or pull request, mentioning content source and licensing information. WAV files are preferred. Other formats should be used only when there is no alternative. (i.e. dataset implementation comes with hardcoded non-wav extension).*
+
+#### Pure Tone
+
+Code:
+
+```python
+waveform = common_utils.get_sinusoid(
+	frequency=300,
+	sample_rate=16000,
+	duration=1,  # seconds
+	n_channels=1,
+	dtype="float32",
+	device="cpu",
+)
+```
+
+#### Noise
+
+Code:
+
+```python
+tensor = common_utils.get_whitenoise()
+```
+
+Files:
+
+* `steam-train-whistle-daniel_simon.wav`
+
+#### Voice
+
+Files:
+
+* `CommonVoice/cv-corpus-4-2019-12-10/tt/clips/common_voice_tt_00000000.mp3`
+* `LibriSpeech/dev-clean/1272/128104/1272-128104-0000.flac`
+* `LJSpeech-1.1/wavs/LJ001-0001.wav`
+* `SpeechCommands/speech_commands_v0.02/go/0a9f9af7_nohash_0.wav`
+* `VCTK-Corpus/wav48/p224/p224_002.wav`
+* `waves_yesno/0_1_0_1_0_1_1_0.wav`
+* `vad-go-stereo-44100.wav`
+* `vad-go-mono-32000.wav`
 
 ## Adding test