DP44/enriched-qwen3-coder-next/DataPRO/FftSharp.Test.md

source_files, generated_at, model, schema_version, sha256

source_files	generated_at	model	schema_version	sha256
DataPRO/FftSharp.Test/PowerSpectralDensityShould.cs	2026-04-16T03:50:52.298896+00:00	Qwen/Qwen3-Coder-Next-FP8	1	bdc792ce4fb3e148

FftSharp.Test

Documentation Page: FftSharp.Test.PowerSpectralDensityShould

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1. Purpose

This test class (PowerSpectralDensityShould) validates the correctness of the FftSharp.Transform.PSD_Welch method — specifically its implementation of the Welch method for power spectral density (PSD) estimation — by comparing its output against a precomputed reference dataset (PSD.csv). It ensures that the computed PSD matches expected frequency bins (FFTfreq) and power values within a defined numerical tolerance, using real-world test data (Raw.csv and PSD.csv). The class serves as a regression guard to prevent unintended changes to the PSD computation behavior.

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2. Public Interface

This is a test fixture (NUnit [TestFixture]) and does not expose production APIs. It contains only private helper methods and test methods. The actual production APIs under test are referenced but not defined here:

• FftSharp.Transform.FFTfreq(int sampleRate, int n)
  Inferred usage: Generates the array of frequency bins (in Hz) for an FFT of length n at given sampleRate. Returns double[].

• FftSharp.Transform.PSD_Welch(double[] data, int sampleRate, WindowType windowType, int windowWidth, double overlappingPct, WindowAveragingType averagingType)
  Inferred usage: Computes the power spectral density of data using Welch’s method. Returns double[] of PSD values (in units of g²/Hz, per test assertions).

  • data: Input time-domain signal.
  • sampleRate: Sampling rate in Hz.
  • windowType: Window function type (e.g., WindowType.Rectangular).
  • windowWidth: Length of each segment (in samples).
  • overlappingPct: Overlap percentage between segments (0–100).
  • averagingType: Averaging strategy (e.g., WindowAveragingType.Averaging).

Note

: The types WindowType and WindowAveragingType are referenced but not defined in this file; their definitions must be found in the FftSharp source.

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3. Invariants

• Data lengths:
  • Raw.csv must contain exactly 304,478 samples per column (RawValueLength = 304478).
  • PSD.csv must contain exactly 2,049 samples per column (PSDValueLength = 2049).
• Frequency bin count: For a signal of length N, the PSD output length is N/2 + 1 (i.e., 2049 for windowWidth = 4096), consistent with real-input FFT symmetry.
• Numerical tolerance: Comparison uses a dynamic epsilon based on the magnitude of the expected value:
  delta = 10^(floor(log10(val1[i]))), adjusted by ±1 in exponent.
  Values < 1e-10 (both expected and actual) are ignored (noise floor).
• Test data format: CSV files use comma separators, with two columns per file (no header), parsed as double.

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4. Dependencies

• External libraries:
  • NUnit.Framework (for [TestFixture], [Test], Assert.Multiple, etc.)
  • System, System.IO, System.Linq, System.Collections.Generic (standard .NET)
• Internal dependencies (inferred from usage):
  • FftSharp.Transform namespace (contains FFTfreq, PSD_Welch)
  • FftSharp.WindowType enum (e.g., Rectangular)
  • FftSharp.WindowAveragingType enum (e.g., Averaging)
• Test data files:
  • Raw.csv: Raw time-domain input (304,478 samples per channel).
  • PSD.csv: Reference PSD output (2,049 Hz and g²/Hz values).
  • Files are loaded relative to TestContext.CurrentContext.TestDirectory.

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5. Gotchas

• Relative tolerance logic: The CloseEnough method uses a relative tolerance scaled by the order of magnitude of the expected value, not a fixed epsilon. This may fail for values near zero or extremely small magnitudes (though those are skipped if both values < 1e-10).
• Hardcoded lengths: RawValueLength and PSDValueLength are constants. If test data files change size, tests will break silently unless updated.
• No validation of PSD_Welch parameters: Tests assume valid inputs (e.g., windowWidth ≤ data.Length, overlappingPct ∈ [0,100]). No tests cover edge cases (e.g., zero overlap vs. 50% overlap, different window types).
• Assumed units: The test compares against g²/Hz, implying the input data is in g (acceleration), but this is not enforced programmatically.
• File path separator: Uses hardcoded "\\" — may fail on non-Windows systems unless TestContext resolves paths correctly.

None identified from source alone beyond the above — but the reliance on external test data and hardcoded constants is a maintenance concern.