From ade9c7fcfc78e2994064627ed9f657c08496fc93 Mon Sep 17 00:00:00 2001
From: Daily Test Coverage Improver
 <github-actions[bot]@users.noreply.github.com>
Date: Sat, 11 Oct 2025 20:37:12 +0000
Subject: [PATCH] Add comprehensive tests for Permutation module
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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- Added 39 new tests covering all Permutation module functions
- Achieved 93.93% coverage for Permutation module (62/66 lines)
- Overall project coverage improved from 4.83% to 6.59% (+1.76pp)
- Total test count: 132 -> 171 tests (+39)

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>
---
 tests/FsMath.Tests/FsMath.Tests.fsproj |   1 +
 tests/FsMath.Tests/PermutationTests.fs | 335 +++++++++++++++++++++++++
 2 files changed, 336 insertions(+)
 create mode 100644 tests/FsMath.Tests/PermutationTests.fs

diff --git a/tests/FsMath.Tests/FsMath.Tests.fsproj b/tests/FsMath.Tests/FsMath.Tests.fsproj
index 675d2e7..9f5dcfa 100644
--- a/tests/FsMath.Tests/FsMath.Tests.fsproj
+++ b/tests/FsMath.Tests/FsMath.Tests.fsproj
@@ -13,6 +13,7 @@
     <Compile Include="VectorIntTests.fs" />
     <Compile Include="VectorManipulationTests.fs" />
     <Compile Include="MatrixFloatTests.fs" />
+    <Compile Include="PermutationTests.fs" />
     <Compile Include="LinearAlgebra.fs" />
     <Compile Include="SpecialFunctions.fs" />
     <Compile Include="Program.fs" />
diff --git a/tests/FsMath.Tests/PermutationTests.fs b/tests/FsMath.Tests/PermutationTests.fs
new file mode 100644
index 0000000..bb44359
--- /dev/null
+++ b/tests/FsMath.Tests/PermutationTests.fs
@@ -0,0 +1,335 @@
+namespace FsMath.Tests.Permutation
+
+open System
+open Xunit
+open FsMath
+open FsMath.Tests.ExpectoStyle
+
+module PermutationTests =
+
+    // ========================================
+    // ofFreshArray tests
+    // ========================================
+
+    [<Fact>]
+    let ``ofFreshArray: creates identity permutation from [0,1,2]`` () =
+        let arr = [| 0; 1; 2 |]
+        let p = Permutation.ofFreshArray arr
+        Assert.Equal(0, p 0)
+        Assert.Equal(1, p 1)
+        Assert.Equal(2, p 2)
+
+    [<Fact>]
+    let ``ofFreshArray: creates valid permutation from [2,0,1]`` () =
+        let arr = [| 2; 0; 1 |]
+        let p = Permutation.ofFreshArray arr
+        Assert.Equal(2, p 0)
+        Assert.Equal(0, p 1)
+        Assert.Equal(1, p 2)
+
+    [<Fact>]
+    let ``ofFreshArray: handles single element [0]`` () =
+        let arr = [| 0 |]
+        let p = Permutation.ofFreshArray arr
+        Assert.Equal(0, p 0)
+
+    [<Fact>]
+    let ``ofFreshArray: handles empty array`` () =
+        let arr = Array.empty<int>
+        let p = Permutation.ofFreshArray arr
+        // Empty permutation should be valid but not callable with any index
+        // (would throw if called)
+        Assert.NotNull(p)
+
+    [<Fact>]
+    let ``ofFreshArray: throws on duplicate indices`` () =
+        let arr = [| 0; 1; 1 |]
+        throws<ArgumentException>(fun () -> Permutation.ofFreshArray arr |> ignore)
+
+    [<Fact>]
+    let ``ofFreshArray: throws on out-of-range negative index`` () =
+        let arr = [| -1; 0; 1 |]
+        throws<ArgumentException>(fun () -> Permutation.ofFreshArray arr |> ignore)
+
+    [<Fact>]
+    let ``ofFreshArray: throws on out-of-range positive index`` () =
+        let arr = [| 0; 1; 3 |]  // 3 is out of range for size 3
+        throws<ArgumentException>(fun () -> Permutation.ofFreshArray arr |> ignore)
+
+    [<Fact>]
+    let ``ofFreshArray: permutation function throws on out-of-range query`` () =
+        let arr = [| 1; 0 |]
+        let p = Permutation.ofFreshArray arr
+        throws<ArgumentException>(fun () -> p 2 |> ignore)
+        throws<ArgumentException>(fun () -> p (-1) |> ignore)
+
+    // ========================================
+    // ofArray tests
+    // ========================================
+
+    [<Fact>]
+    let ``ofArray: creates valid permutation`` () =
+        let arr = [| 1; 2; 0 |]
+        let p = Permutation.ofArray arr
+        Assert.Equal(1, p 0)
+        Assert.Equal(2, p 1)
+        Assert.Equal(0, p 2)
+
+    [<Fact>]
+    let ``ofArray: does not modify original array`` () =
+        let arr = [| 1; 2; 0 |]
+        let original = Array.copy arr
+        let p = Permutation.ofArray arr
+        // Ensure original array unchanged
+        Assert.Equal<int[]>(original, arr)
+
+    // ========================================
+    // sign tests
+    // ========================================
+
+    [<Fact>]
+    let ``sign: identity permutation has sign +1`` () =
+        let p = Permutation.identity
+        let s = Permutation.sign 3 p
+        Assert.Equal(1.0, s)
+
+    [<Fact>]
+    let ``sign: single transposition has sign -1`` () =
+        // Swap 0 and 1: [1, 0, 2]
+        let p = Permutation.swap 0 1
+        let s = Permutation.sign 3 p
+        Assert.Equal(-1.0, s)
+
+    [<Fact>]
+    let ``sign: two transpositions has sign +1`` () =
+        // [1, 0, 2] then swap 1 and 2 -> [1, 2, 0]
+        let arr = [| 1; 2; 0 |]
+        let p = Permutation.ofArray arr
+        let s = Permutation.sign 3 p
+        // This is a 3-cycle: 0->1->2->0, which is (n-1) = 2 transpositions, so sign is +1
+        Assert.Equal(1.0, s)
+
+    [<Fact>]
+    let ``sign: reversal of size 2 has sign -1`` () =
+        let p = Permutation.reversal 2
+        let s = Permutation.sign 2 p
+        Assert.Equal(-1.0, s)
+
+    [<Fact>]
+    let ``sign: reversal of size 3 has sign -1`` () =
+        let p = Permutation.reversal 3
+        let s = Permutation.sign 3 p
+        // Reversal [2,1,0] has 1 cycle (0->2->0) and 1 fixed point (1),
+        // so 3-2=1 transposition, sign = -1
+        Assert.Equal(-1.0, s)
+
+    // ========================================
+    // ofPairs tests
+    // ========================================
+
+    [<Fact>]
+    let ``ofPairs: creates permutation from pairs`` () =
+        let p = Permutation.ofPairs [(0, 2); (2, 1)]
+        Assert.Equal(2, p 0)
+        Assert.Equal(1, p 2)
+
+    [<Fact>]
+    let ``ofPairs: unmapped indices map to themselves`` () =
+        let p = Permutation.ofPairs [(0, 1)]
+        Assert.Equal(1, p 0)
+        Assert.Equal(2, p 2)  // unmapped
+        Assert.Equal(5, p 5)  // unmapped
+
+    [<Fact>]
+    let ``ofPairs: empty pairs creates identity`` () =
+        let p = Permutation.ofPairs []
+        Assert.Equal(0, p 0)
+        Assert.Equal(5, p 5)
+
+    // ========================================
+    // swap tests
+    // ========================================
+
+    [<Fact>]
+    let ``swap: exchanges two indices`` () =
+        let p = Permutation.swap 1 3
+        Assert.Equal(3, p 1)
+        Assert.Equal(1, p 3)
+
+    [<Fact>]
+    let ``swap: leaves other indices unchanged`` () =
+        let p = Permutation.swap 1 3
+        Assert.Equal(0, p 0)
+        Assert.Equal(2, p 2)
+        Assert.Equal(4, p 4)
+
+    [<Fact>]
+    let ``swap: swapping same index is identity`` () =
+        let p = Permutation.swap 2 2
+        Assert.Equal(2, p 2)
+
+    // ========================================
+    // reversal tests
+    // ========================================
+
+    [<Fact>]
+    let ``reversal: size 1 reverses to itself`` () =
+        let p = Permutation.reversal 1
+        Assert.Equal(0, p 0)
+
+    [<Fact>]
+    let ``reversal: size 3 reverses indices`` () =
+        let p = Permutation.reversal 3
+        Assert.Equal(2, p 0)
+        Assert.Equal(1, p 1)
+        Assert.Equal(0, p 2)
+
+    [<Fact>]
+    let ``reversal: size 5 reverses indices`` () =
+        let p = Permutation.reversal 5
+        Assert.Equal(4, p 0)
+        Assert.Equal(3, p 1)
+        Assert.Equal(2, p 2)
+        Assert.Equal(1, p 3)
+        Assert.Equal(0, p 4)
+
+    [<Fact>]
+    let ``reversal: throws on non-positive size`` () =
+        throws<ArgumentException>(fun () -> Permutation.reversal 0 |> ignore)
+        throws<ArgumentException>(fun () -> Permutation.reversal -1 |> ignore)
+
+    // ========================================
+    // rotation tests
+    // ========================================
+
+    [<Fact>]
+    let ``rotation: distance 0 is identity`` () =
+        let p = Permutation.rotation 5 0
+        Assert.Equal(0, p 0)
+        Assert.Equal(1, p 1)
+        Assert.Equal(4, p 4)
+
+    [<Fact>]
+    let ``rotation: positive distance rotates right`` () =
+        let p = Permutation.rotation 5 2
+        Assert.Equal(2, p 0)
+        Assert.Equal(3, p 1)
+        Assert.Equal(0, p 3)  // wraps around
+        Assert.Equal(1, p 4)  // wraps around
+
+    [<Fact>]
+    let ``rotation: negative distance rotates left`` () =
+        let p = Permutation.rotation 5 -1
+        Assert.Equal(4, p 0)  // wraps around
+        Assert.Equal(0, p 1)
+        Assert.Equal(1, p 2)
+        Assert.Equal(3, p 4)
+
+    [<Fact>]
+    let ``rotation: full rotation throws exception`` () =
+        // This should throw because distance >= size
+        throws<ArgumentException>(fun () -> Permutation.rotation 5 5 |> ignore)
+
+    [<Fact>]
+    let ``rotation: throws on non-positive size`` () =
+        throws<ArgumentException>(fun () -> Permutation.rotation 0 1 |> ignore)
+        throws<ArgumentException>(fun () -> Permutation.rotation -1 1 |> ignore)
+
+    [<Fact>]
+    let ``rotation: throws on distance >= size`` () =
+        throws<ArgumentException>(fun () -> Permutation.rotation 5 5 |> ignore)
+        throws<ArgumentException>(fun () -> Permutation.rotation 5 6 |> ignore)
+        throws<ArgumentException>(fun () -> Permutation.rotation 5 -5 |> ignore)
+
+    // ========================================
+    // identity tests
+    // ========================================
+
+    [<Fact>]
+    let ``identity: maps every index to itself`` () =
+        let p = Permutation.identity
+        Assert.Equal(0, p 0)
+        Assert.Equal(1, p 1)
+        Assert.Equal(100, p 100)
+        Assert.Equal(-5, p -5)
+
+    // ========================================
+    // inverse tests
+    // ========================================
+
+    [<Fact>]
+    let ``inverse: of identity is identity`` () =
+        let p = Permutation.identity
+        let pInv = Permutation.inverse 5 p
+        Assert.Equal(0, pInv 0)
+        Assert.Equal(1, pInv 1)
+        Assert.Equal(4, pInv 4)
+
+    [<Fact>]
+    let ``inverse: of swap is itself`` () =
+        let p = Permutation.swap 1 3
+        let pInv = Permutation.inverse 5 p
+        Assert.Equal(3, pInv 1)
+        Assert.Equal(1, pInv 3)
+        Assert.Equal(0, pInv 0)
+        Assert.Equal(2, pInv 2)
+
+    [<Fact>]
+    let ``inverse: of [2,0,1] is [1,2,0]`` () =
+        // p: 0->2, 1->0, 2->1
+        // pInv: 0->1, 1->2, 2->0
+        let arr = [| 2; 0; 1 |]
+        let p = Permutation.ofArray arr
+        let pInv = Permutation.inverse 3 p
+        Assert.Equal(1, pInv 0)
+        Assert.Equal(2, pInv 1)
+        Assert.Equal(0, pInv 2)
+
+    [<Fact>]
+    let ``inverse: applying p then pInv returns identity`` () =
+        let arr = [| 1; 2; 0; 4; 3 |]
+        let p = Permutation.ofArray arr
+        let pInv = Permutation.inverse 5 p
+
+        // p(pInv(i)) should equal i for all i
+        for i in 0..4 do
+            Assert.Equal(i, p(pInv i))
+            Assert.Equal(i, pInv(p i))
+
+    [<Fact>]
+    let ``inverse: throws on non-positive size`` () =
+        let p = Permutation.identity
+        throws<ArgumentException>(fun () -> Permutation.inverse 0 p |> ignore)
+        throws<ArgumentException>(fun () -> Permutation.inverse -1 p |> ignore)
+
+    // ========================================
+    // Composition and algebraic properties
+    // ========================================
+
+    [<Fact>]
+    let ``composition: two swaps`` () =
+        let p1 = Permutation.swap 0 1
+        let p2 = Permutation.swap 1 2
+        let composed = fun i -> p2 (p1 i)
+
+        // p1: 0->1, 1->0, 2->2
+        // p2: 0->0, 1->2, 2->1
+        // composed: 0->p2(1)=2, 1->p2(0)=0, 2->p2(2)=1
+        Assert.Equal(2, composed 0)
+        Assert.Equal(0, composed 1)
+        Assert.Equal(1, composed 2)
+
+    [<Fact>]
+    let ``composition: rotation then reversal`` () =
+        let p1 = Permutation.rotation 4 1  // [1,2,3,0]
+        let p2 = Permutation.reversal 4    // [3,2,1,0]
+        let composed = fun i -> p2 (p1 i)
+
+        // p1(0)=1, p2(1)=2
+        Assert.Equal(2, composed 0)
+        // p1(1)=2, p2(2)=1
+        Assert.Equal(1, composed 1)
+        // p1(2)=3, p2(3)=0
+        Assert.Equal(0, composed 2)
+        // p1(3)=0, p2(0)=3
+        Assert.Equal(3, composed 3)