[test] Adding missing BidirectionalCollection::partition(subrange:) and MutableCollection::partition(subrange:) unit tests (#95)

Author: LucianoPAlmeida

Tests/SwiftAlgorithmsTests/PartitionTests.swift

@@ -64,14 +64,17 @@ final class PartitionTests: XCTestCase {
   func testStablePartitionWithSubrange() {
     for length in 10...20 {
       let a = Array(0..<length)
-      for j in 0..<length {
-        var b = a
-        let partitionRange = 0..<j
-        let condition = { $0 < j - 1 }
-        let p = b.stablePartition(subrange: partitionRange, by: condition)
-        XCTAssertEqual(p, partitionRange.count > 0 ? 1 : 0)
-        XCTAssertEqualSequences(b[partitionRange.lowerBound..<p], a[partitionRange].filter { !condition($0) })
-        XCTAssertEqualSequences(b[p..<partitionRange.upperBound], a[partitionRange].filter(condition))
+      for i in 0..<length {
+        for j in 0...i {
+          var b = a
+          let partitionRange = j..<i
+          let condition = { $0 < i - 1 }
+          let p = b.stablePartition(subrange: partitionRange, by: condition)
+
+          XCTAssertEqual(p, partitionRange.count == 0 ? j : j + 1)
+          XCTAssertEqualSequences(b[partitionRange.lowerBound..<p], a[partitionRange].filter { !condition($0) })
+          XCTAssertEqualSequences(b[p..<partitionRange.upperBound], a[partitionRange].filter(condition))
+        }
       }
     }
   }
@@ -88,4 +91,46 @@ final class PartitionTests: XCTestCase {
       }
     }
   }
+  
+  func testPartitionWithSubrangeBidirectionalCollection() {
+    for length in 10...20 {
+      let a = Array(0..<length)
+      for i in 0..<length {
+        for j in 0...i {
+          var b = a
+          let partitionRange = j..<i
+          let condition = { $0 < i - 1 }
+          let p = b.partition(subrange: partitionRange, by: condition)
+          
+          XCTAssertEqual(p, partitionRange.count == 0 ? j : j + 1)
+          XCTAssertEqualSequences(b[partitionRange.lowerBound..<p], a[partitionRange].filter { !condition($0) })
+          XCTAssertUnorderedEqualSequences(b[p..<partitionRange.upperBound], a[partitionRange].filter(condition))
+        }
+      }
+    }
+  }
+
+  func testPartitionWithSubrangeMutableCollection() {
+    for length in 10...20 {
+      let a = Array(0..<length)
+      for i in 0..<length {
+        for j in 0...i {
+          var b = a.eraseToAnyMutableCollection()
+          var bdc = a
+          let partitionRange = j..<i
+          let condition = { $0 < i - 1 }
+          let p = b.partition(subrange: partitionRange, by: condition)
+          let bdcp = bdc.partition(subrange: partitionRange, by: condition)
+          
+          XCTAssertEqual(p, partitionRange.count == 0 ? j : j + 1)
+          XCTAssertEqualSequences(b[partitionRange.lowerBound..<p], a[partitionRange].filter { !condition($0) })
+          XCTAssertUnorderedEqualSequences(b[p..<partitionRange.upperBound], a[partitionRange].filter(condition))
+          
+          // Must produce the same result as the `BidirectionalCollection` specialized overload.
+          XCTAssertEqualSequences(b[partitionRange.lowerBound..<p], bdc[partitionRange.lowerBound..<bdcp])
+          XCTAssertUnorderedEqualSequences(b[p..<partitionRange.upperBound], bdc[bdcp..<partitionRange.upperBound])
+        }
+      }
+    }
+  }
 }

Tests/SwiftAlgorithmsTests/TestUtilities.swift

@@ -46,6 +46,34 @@ struct SplitMix64: RandomNumberGenerator {
   }
 }
 
+// An eraser helper to any mutable collection
+struct AnyMutableCollection<Base> where Base: MutableCollection {
+  var base: Base
+}
+
+extension AnyMutableCollection: MutableCollection {
+  typealias Index = Base.Index
+  typealias Element = Base.Element
+  
+  var startIndex: Base.Index { base.startIndex }
+  var endIndex: Base.Index { base.endIndex }
+
+  func index(after i: Index) -> Index {
+    return base.index(after: i)
+  }
+
+  subscript(position: Base.Index) -> Base.Element {
+    _read { yield base[position] }
+    set { base[position] = newValue }
+  }
+}
+
+extension MutableCollection {
+  func eraseToAnyMutableCollection() -> AnyMutableCollection<Self> {
+    AnyMutableCollection(base: self)
+  }
+}
+
 func XCTAssertEqualSequences<S1: Sequence, S2: Sequence>(
   _ expression1: @autoclosure () throws -> S1,
   _ expression2: @autoclosure () throws -> S2,
@@ -56,6 +84,33 @@ func XCTAssertEqualSequences<S1: Sequence, S2: Sequence>(
     message(), file: file, line: line)
 }
 
+// Two sequences contains exactly the same element but not necessarily in the same order.
+func XCTAssertUnorderedEqualSequences<S1: Sequence, S2: Sequence>(
+  _ expression1: @autoclosure () throws -> S1,
+  _ expression2: @autoclosure () throws -> S2,
+  file: StaticString = #file, line: UInt = #line
+) rethrows where S1.Element: Equatable, S1.Element == S2.Element {
+  var s1 = Array(try expression1())
+  var missing: [S1.Element] = []
+  for elt in try expression2() {
+    guard let idx = s1.firstIndex(of: elt) else {
+      missing.append(elt)
+      continue
+    }
+    s1.remove(at: idx)
+  }
+  
+  XCTAssertTrue(
+    missing.isEmpty, "first sequence missing '\(missing)' elements from second sequence",
+    file: file, line: line
+  )
+
+  XCTAssertTrue(
+    s1.isEmpty, "first sequence contains \(s1) missing from second sequence",
+    file: file, line: line
+  )
+}
+
 func XCTAssertEqualSequences<S1: Sequence, S2: Sequence>(
   _ expression1: @autoclosure () throws -> S1,
   _ expression2: @autoclosure () throws -> S2,