diff --git a/Tests/PenguinCSVTests/CSVInterpreterTests.swift b/Tests/PenguinCSVTests/CSVInterpreterTests.swift
index 27df837c..7aaeffd5 100644
--- a/Tests/PenguinCSVTests/CSVInterpreterTests.swift
+++ b/Tests/PenguinCSVTests/CSVInterpreterTests.swift
@@ -290,6 +290,37 @@ final class CSVInterpreterTests: XCTestCase {
   ]
 }
 
+#if swift(>=5.3)
+fileprivate func assertCompatible(
+  _ cell: String, with type: CSVType, file: StaticString = #filePath, line: UInt = #line
+) {
+  XCTAssert(
+    type.isCompatibleWith(cell), "\(type) should be compatible with \(cell)", file: file, line: line
+  )
+}
+
+fileprivate func assertNotCompatible(
+  _ cell: String, with type: CSVType, file: StaticString = #filePath, line: UInt = #line
+) {
+  XCTAssertFalse(
+    type.isCompatibleWith(cell), "\(type) should not be compatible with \(cell)", file: file,
+    line: line)
+}
+
+fileprivate func assertParsedHeuristics(
+  _ text: String, _ heuristics: [SeparatorHeuristics], file: StaticString = #file,
+  line: UInt = #line
+) {
+  var text2 = text  // Make a mutable copy, as withUTF8 might modify the string.
+  text2.withUTF8 { body in
+    let lines = body.split(separator: UInt8(ascii: "\n"))
+    precondition(lines.count > 2)
+    let fullLines = lines[0..<lines.count - 1]  // Drop last linee as it could be incomplete.
+    let separatorHeuristics = computeSeparatorHeuristics(fullLines)
+    assertEqual(heuristics, separatorHeuristics, file: file, line: line)
+  }
+}
+#else
 fileprivate func assertCompatible(
   _ cell: String, with type: CSVType, file: StaticString = #file, line: UInt = #line
 ) {
@@ -319,6 +350,7 @@ fileprivate func assertParsedHeuristics(
     assertEqual(heuristics, separatorHeuristics, file: file, line: line)
   }
 }
+#endif
 
 fileprivate func assertEqual(
   _ expected: [SeparatorHeuristics], _ actual: [SeparatorHeuristics], file: StaticString, line: UInt
@@ -337,6 +369,72 @@ fileprivate func assertEqual(
   }
 }
 
+#if swift(>=5.3)
+fileprivate func checkColumnGuesser(
+  expected: [CSVType], best: CSVType, cells: String..., file: StaticString = #filePath,
+  line: UInt = #line
+) {
+  var guesser = CSVColumnGuesser()
+  for cell in cells {
+    guesser.updateCompatibilities(cell: cell)
+  }
+  XCTAssertEqual(Set(expected), guesser.possibleTypes, "Cells: \(cells)", file: file, line: line)
+  XCTAssertEqual(best, guesser.bestGuess, "Cells: \(cells)", file: file, line: line)
+}
+
+fileprivate func checkColumnSniffing(
+  withoutFirstRow: [CSVType],
+  withFirstRow: [CSVType],
+  _ contents: String,
+  separator: Unicode.Scalar = ",",
+  file: StaticString = #filePath,
+  line: UInt = #line
+) {
+  precondition(
+    withoutFirstRow.count == withFirstRow.count,
+    "Mismatched counts: \(withoutFirstRow.count) and \(withFirstRow.count)")
+  var c = contents  // Must make a mutable copy first. :-(
+  c.withUTF8 { contents in
+    let lines = contents.split(separator: UInt8(ascii: "\n"))
+    let allLines = lines[0..<lines.count]  // Don't drop the last one in tests!
+    let result = try! computeColumnTypes(
+      allLines, separator: separator, columnCount: withoutFirstRow.count)
+    XCTAssertEqual(
+      withoutFirstRow, result.withoutFirstRow.map { $0.bestGuess }, "Without first row problems!",
+      file: file, line: line)
+    XCTAssertEqual(
+      withFirstRow, result.withFirstRow.map { $0.bestGuess }, "With first row problems!",
+      file: file, line: line)
+  }
+}
+
+fileprivate func checkComputeColumnNames(
+  expected: [String], separator: Unicode.Scalar = ",", _ contents: String,
+  file: StaticString = #filePath, line: UInt = #line
+) {
+  var c = contents
+  c.withUTF8 { contents in
+    let lines = contents.split(separator: UInt8(ascii: "\n"))
+    let result = try! computeColumnNames(
+      headerRow: lines[0], separator: separator, columnCount: expected.count)
+    XCTAssertEqual(expected, result, file: file, line: line)
+  }
+}
+
+fileprivate func assertColumnNames(
+  _ expected: [String], _ result: CSVGuess, file: StaticString = #filePath, line: UInt = #line
+) {
+  let actual = result.columns.map { $0.name }
+  XCTAssertEqual(expected, actual, file: file, line: line)
+}
+
+fileprivate func assertColumnTypes(
+  _ expected: [CSVType], _ result: CSVGuess, file: StaticString = #filePath, line: UInt = #line
+) {
+  let actual = result.columns.map { $0.type }
+  XCTAssertEqual(expected, actual, file: file, line: line)
+}
+#else
 fileprivate func checkColumnGuesser(
   expected: [CSVType], best: CSVType, cells: String..., file: StaticString = #file,
   line: UInt = #line
@@ -401,6 +499,7 @@ fileprivate func assertColumnTypes(
   let actual = result.columns.map { $0.type }
   XCTAssertEqual(expected, actual, file: file, line: line)
 }
+#endif
 
 extension SeparatorHeuristics {
   fileprivate init(
diff --git a/Tests/PenguinCSVTests/CSVReaderTests.swift b/Tests/PenguinCSVTests/CSVReaderTests.swift
index d6ad89b5..31e43da7 100644
--- a/Tests/PenguinCSVTests/CSVReaderTests.swift
+++ b/Tests/PenguinCSVTests/CSVReaderTests.swift
@@ -258,6 +258,15 @@ fileprivate enum TestError: Error {
   case missingMetadata
 }
 
+#if swift(>=5.3)
+fileprivate func assertMetadataNotNil(
+  _ reader: CSVReader, file: StaticString = #filePath, line: UInt = #line
+) throws -> CSVGuess {
+  XCTAssertNotNil(reader.metadata, file: file, line: line)
+  guard let metadata = reader.metadata else { throw TestError.missingMetadata }
+  return metadata
+}
+#else
 fileprivate func assertMetadataNotNil(
   _ reader: CSVReader, file: StaticString = #file, line: UInt = #line
 ) throws -> CSVGuess {
@@ -265,3 +274,4 @@ fileprivate func assertMetadataNotNil(
   guard let metadata = reader.metadata else { throw TestError.missingMetadata }
   return metadata
 }
+#endif
diff --git a/Tests/PenguinParallelTests/NonBlockingThreadPoolTests.swift b/Tests/PenguinParallelTests/NonBlockingThreadPoolTests.swift
index 450d6951..81ca845e 100644
--- a/Tests/PenguinParallelTests/NonBlockingThreadPoolTests.swift
+++ b/Tests/PenguinParallelTests/NonBlockingThreadPoolTests.swift
@@ -110,6 +110,17 @@ final class NonBlockingThreadPoolTests: XCTestCase {
 }
 
 // Overload for 2-tuple
+#if swift(>=5.3)
+fileprivate func XCTAssertEqual(
+  _ lhs: (Int, Int), _ rhs: (Int, Int), _ msg: String = "", file: StaticString = #filePath,
+  line: UInt = #line
+) {
+  XCTAssertEqual(
+    lhs.0, rhs.0, "items 0 did not agree: \(lhs) vs \(rhs) \(msg)", file: file, line: line)
+  XCTAssertEqual(
+    lhs.1, rhs.1, "items 1 did not agree: \(lhs) vs \(rhs) \(msg)", file: file, line: line)
+}
+#else
 fileprivate func XCTAssertEqual(
   _ lhs: (Int, Int), _ rhs: (Int, Int), _ msg: String = "", file: StaticString = #file,
   line: UInt = #line
@@ -119,6 +130,7 @@ fileprivate func XCTAssertEqual(
   XCTAssertEqual(
     lhs.1, rhs.1, "items 1 did not agree: \(lhs) vs \(rhs) \(msg)", file: file, line: line)
 }
+#endif
 
 /// A platform to count threads and to ensure deallocation.
 ///
diff --git a/Tests/PenguinTablesTests/CSVParsibleTests.swift b/Tests/PenguinTablesTests/CSVParsibleTests.swift
index 25b377c9..36bed794 100644
--- a/Tests/PenguinTablesTests/CSVParsibleTests.swift
+++ b/Tests/PenguinTablesTests/CSVParsibleTests.swift
@@ -30,6 +30,20 @@ final class CSVParsibleTests: XCTestCase {
   ]
 }
 
+#if swift(>=5.3)
+fileprivate func assertParse<T: PCSVParsible & Equatable>(
+  _ bytes: String,
+  as val: T,
+  file: StaticString = #filePath,
+  line: UInt = #line
+) {
+  var s = bytes
+  s.withUTF8 { s in
+    let parsed = T(CSVCell.raw(s))
+    XCTAssertEqual(parsed, val, file: file, line: line)
+  }
+}
+#else
 fileprivate func assertParse<T: PCSVParsible & Equatable>(
   _ bytes: String,
   as val: T,
@@ -42,3 +56,4 @@ fileprivate func assertParse<T: PCSVParsible & Equatable>(
     XCTAssertEqual(parsed, val, file: file, line: line)
   }
 }
+#endif
diff --git a/Tests/PenguinTablesTests/StringParsibleTests.swift b/Tests/PenguinTablesTests/StringParsibleTests.swift
index 9655fcdb..b0d020f1 100644
--- a/Tests/PenguinTablesTests/StringParsibleTests.swift
+++ b/Tests/PenguinTablesTests/StringParsibleTests.swift
@@ -67,6 +67,37 @@ final class StringParsibleTests: XCTestCase {
   ]
 }
 
+#if swift(>=5.3)
+fileprivate func assertParses<T: PStringParsible & Equatable>(
+  expected: T, source: String, file: StaticString = #filePath, line: UInt = #line
+) {
+  let result = T(parsing: source)
+  XCTAssertEqual(expected, result, file: file, line: line)
+}
+
+fileprivate func assertParseFailure<T: PStringParsible>(
+  a type: T.Type,
+  from source: String,
+  reason: String? = nil,
+  file: StaticString = #filePath,
+  line: UInt = #line
+) {
+  do {
+    let unexpected = try T(parseOrThrow: source)
+    XCTFail(
+      "\"\(source)\" parsed as \(type) unexpectedly as \(unexpected).", file: file, line: line)
+  } catch {
+    let msg = String(describing: error)
+    if let reason = reason {
+      XCTAssert(
+        msg.contains(reason),
+        "Error message \"\(msg)\" did not contain expected string \"\(reason)\".",
+        file: file,
+        line: line)
+    }
+  }
+}
+#else
 fileprivate func assertParses<T: PStringParsible & Equatable>(
   expected: T, source: String, file: StaticString = #file, line: UInt = #line
 ) {
@@ -96,3 +127,4 @@ fileprivate func assertParseFailure<T: PStringParsible>(
     }
   }
 }
+#endif
diff --git a/Tests/PenguinTablesTests/TableTests.swift b/Tests/PenguinTablesTests/TableTests.swift
index 0573ce9d..13177b95 100644
--- a/Tests/PenguinTablesTests/TableTests.swift
+++ b/Tests/PenguinTablesTests/TableTests.swift
@@ -277,8 +277,10 @@ final class TableTests: XCTestCase {
   ]
 }
 
+#if swift(>=5.3)
 fileprivate func assertPColumnsEqual<T: ElementRequirements>(
-  _ lhs: PColumn?, _ rhs: PColumn?, dtype: T.Type, file: StaticString = #file, line: UInt = #line
+  _ lhs: PColumn?, _ rhs: PColumn?, dtype: T.Type,
+  file: StaticString = #filePath, line: UInt = #line
 ) {
   if lhs == nil && rhs == nil { return }
 
@@ -296,3 +298,25 @@ fileprivate func assertPColumnsEqual<T: ElementRequirements>(
   }
   XCTAssertEqual(lhsT, rhsT, file: file, line: line)
 }
+#else
+fileprivate func assertPColumnsEqual<T: ElementRequirements>(
+  _ lhs: PColumn?, _ rhs: PColumn?, dtype: T.Type,
+  file: StaticString = #file, line: UInt = #line
+) {
+  if lhs == nil && rhs == nil { return }
+
+  guard let lhsT: PTypedColumn<T> = try? lhs?.asDType() else {
+    XCTFail(
+      "lhs could not be interpreted as dtype \(dtype): \(String(describing: lhs))",
+      file: file, line: line)
+    return
+  }
+  guard let rhsT: PTypedColumn<T> = try? rhs?.asDType() else {
+    XCTFail(
+      "rhs could not be interpreted as dtype \(dtype): \(String(describing: rhs))",
+      file: file, line: line)
+    return
+  }
+  XCTAssertEqual(lhsT, rhsT, file: file, line: line)
+}
+#endif