fix: Correct wrong default periods in obsolete GetPvo (#2214)

Author: DaveSkender

docs/migration/v3.md

@@ -75,6 +75,12 @@ defect versus changing intended behavior](https://github.com/facioquo/stock-indi
   `ToPrs()` and pre-`3.0.0` behavior. **If you called `GetPrs()` on `3.0.x`, stored values and any
   thresholds tuned against them must be revalidated; new values are the reciprocal of
   old ones.** Callers of `ToPrs()` were never affected.
+- **`GetPvo()` used the wrong default periods.** The shim declared
+  `fastPeriods: 9, slowPeriods: 12` where both v2 and `ToPvo()` declare `12` and `26`,
+  so calling `GetPvo()` with no arguments silently computed a differently-parameterized
+  PVO. Corrected in `3.0.1`. **If you called `GetPvo()` without explicit periods on `3.0.x`, stored values
+  must be revalidated.** Callers who passed explicit periods, and callers of `ToPvo()`,
+  were never affected.
 - **`GetPrs()` with no `lookbackPeriods` threw.** The unspecified lookback was mapped to
   `0`, which validation rejects, so the shim's own default raised
   `ArgumentOutOfRangeException`. As of `3.0.1` it computes with a null `PrsPercent`, as

src/Obsolete.V3.Indicators.cs

@@ -724,7 +724,7 @@ public static IEnumerable<PrsResult> GetPrs(
     [Obsolete("Rename `GetPvo(..)` to `ToPvo(..)`", false)]
     public static IEnumerable<PvoResult> GetPvo(
         this IEnumerable<IBar> bars,
-        int fastPeriods = 9, int slowPeriods = 12, int signalPeriods = 9)
+        int fastPeriods = 12, int slowPeriods = 26, int signalPeriods = 9)
         => bars.ToSortedList().ToPvo(fastPeriods, slowPeriods, signalPeriods);
 
     [ExcludeFromCodeCoverage]

tests/Library/Indicators/k-q/Pvo/PvoObsoleteShimTests.cs

@@ -0,0 +1,69 @@
+namespace StaticSeries;
+
+/// <summary>
+/// Tests for the obsolete v3 <c>GetPvo</c> shim, which must return what the pre-3.0.0
+/// API returned.
+/// </summary>
+/// <remarks>
+/// The shim declared <c>9, 12, 9</c> where both v2 and <c>ToPvo</c> declare
+/// <c>12, 26, 9</c> — the correct values shifted one position. Calling the documented
+/// default therefore computed a different indicator, silently: the result is a
+/// well-formed PVO, just not the one asked for. Nothing here called the shim, so
+/// nothing caught it.
+/// </remarks>
+[TestClass]
+public class PvoObsoleteShimTests : TestBaseWithPrecision
+{
+    [TestMethod]
+    public void GetPvoDefaultsMatchToPvo()
+    {
+#pragma warning disable CS0618 // exercising the obsolete shim is the point
+        List<PvoResult> shim = Bars.GetPvo().ToList();
+#pragma warning restore CS0618
+
+        IReadOnlyList<PvoResult> expected = Bars.ToPvo();
+
+        shim.Should().HaveCount(expected.Count);
+        shim.Select(static r => r.Pvo).Should().Equal(expected.Select(static r => r.Pvo));
+        shim.Select(static r => r.Signal).Should().Equal(expected.Select(static r => r.Signal));
+        shim.Select(static r => r.Histogram).Should().Equal(expected.Select(static r => r.Histogram));
+    }
+
+    [TestMethod]
+    public void GetPvoDefaultsAreNotTheShiftedPeriods()
+    {
+        // guards the specific 3.0.0 regression: the shim declared 9, 12, 9
+#pragma warning disable CS0618
+        List<PvoResult> shim = Bars.GetPvo().ToList();
+#pragma warning restore CS0618
+
+        IReadOnlyList<PvoResult> shifted = Bars.ToPvo(9, 12, 9);
+
+        shim[^1].Pvo.Should().NotBeApproximately(shifted[^1].Pvo!.Value, Money6);
+    }
+
+    [TestMethod]
+    public void GetPvoMatchesKnownValues()
+    {
+        // anchors the shim to absolute values, so a co-regression in ToPvo cannot
+        // move both sides of the comparison above and pass unnoticed
+#pragma warning disable CS0618
+        List<PvoResult> shim = Bars.GetPvo().ToList();
+#pragma warning restore CS0618
+
+        shim.Should().HaveCount(502);
+        shim[501].Pvo.Should().BeApproximately(10.439509, Money6);
+    }
+
+    [TestMethod]
+    public void GetPvoWithExplicitPeriodsMatchesToPvo()
+    {
+#pragma warning disable CS0618
+        List<PvoResult> shim = Bars.GetPvo(10, 20, 7).ToList();
+#pragma warning restore CS0618
+
+        IReadOnlyList<PvoResult> expected = Bars.ToPvo(10, 20, 7);
+
+        shim.Select(static r => r.Pvo).Should().Equal(expected.Select(static r => r.Pvo));
+    }
+}