diff --git a/Sources/XcodeProj/Scheme/XCScheme+TestableReference.swift b/Sources/XcodeProj/Scheme/XCScheme+TestableReference.swift
index 39a4696b..23c5413b 100644
--- a/Sources/XcodeProj/Scheme/XCScheme+TestableReference.swift
+++ b/Sources/XcodeProj/Scheme/XCScheme+TestableReference.swift
@@ -33,6 +33,24 @@ public extension XCScheme {
             self.selectedTests = selectedTests
             self.skippedTests = skippedTests
         }
+      
+        public init(skipped: Bool,
+                    parallelizable: Bool = false,
+                    randomExecutionOrdering: Bool = false,
+                    buildableReference: BuildableReference,
+                    locationScenarioReference: LocationScenarioReference? = nil,
+                    skippedTests: [TestItem] = [],
+                    selectedTests: [TestItem] = [],
+                    useTestSelectionWhitelist: Bool? = nil) {
+            self.skipped = skipped
+            self.parallelizable = parallelizable ? .all : .none
+            self.randomExecutionOrdering = randomExecutionOrdering
+            self.buildableReference = buildableReference
+            self.locationScenarioReference = locationScenarioReference
+            self.useTestSelectionWhitelist = useTestSelectionWhitelist
+            self.selectedTests = selectedTests
+            self.skippedTests = skippedTests
+        }
 
         init(element: AEXMLElement) throws {
             skipped = element.attributes["skipped"] == "YES"
diff --git a/Tests/XcodeProjTests/Scheme/XCSchemeTests.swift b/Tests/XcodeProjTests/Scheme/XCSchemeTests.swift
index 83a32735..6930fc80 100644
--- a/Tests/XcodeProjTests/Scheme/XCSchemeTests.swift
+++ b/Tests/XcodeProjTests/Scheme/XCSchemeTests.swift
@@ -58,6 +58,12 @@ final class XCSchemeIntegrationTests: XCTestCase {
         }
     }
 
+    func test_read_iosScheme_noParallelizable_setsswiftTestingOnly() throws {
+        let scheme = try XCScheme(path: iosSchemePath)
+
+        XCTAssertEqual(scheme.testAction?.testables.first?.parallelizable, .swiftTestingOnly)
+    }
+
     func test_write_minimalScheme() {
         testWrite(from: minimalSchemePath,
                   initModel: { try? XCScheme(path: $0) },
@@ -85,7 +91,7 @@ final class XCSchemeIntegrationTests: XCTestCase {
         XCTAssertNil(subject.attributes["useTestSelectionWhitelist"])
     }
 
-    func test_write_testableReferenceAttributesValues() {
+    func test_write_testableReferenceAttributesValues_allParallelizable() {
         let reference = XCScheme.TestableReference(
             skipped: false,
             parallelizable: .all,
@@ -106,28 +112,72 @@ final class XCSchemeIntegrationTests: XCTestCase {
         XCTAssertEqual(subject.attributes["useTestSelectionWhitelist"], "YES")
         XCTAssertEqual(subject.attributes["testExecutionOrdering"], "random")
     }
-  
-  func test_write_testableReferenceAttributesValuesForSwiftTesting() {
-      let reference = XCScheme.TestableReference(
-          skipped: false,
-          parallelizable: .swiftTestingOnly,
-          randomExecutionOrdering: true,
-          buildableReference: XCScheme.BuildableReference(
-              referencedContainer: "",
-              blueprint: PBXObject(),
-              buildableName: "",
-              blueprintName: ""
-          ),
-          skippedTests: [],
-          selectedTests: [],
-          useTestSelectionWhitelist: true
-      )
-      let subject = reference.xmlElement()
-      XCTAssertEqual(subject.attributes["skipped"], "NO")
-      XCTAssertNil(subject.attributes["parallelizable"])
-      XCTAssertEqual(subject.attributes["useTestSelectionWhitelist"], "YES")
-      XCTAssertEqual(subject.attributes["testExecutionOrdering"], "random")
-  }
+
+    func test_write_testableReferenceAttributesValues_noneParallelizable() {
+        let reference = XCScheme.TestableReference(
+            skipped: false,
+            parallelizable: .none,
+            randomExecutionOrdering: true,
+            buildableReference: XCScheme.BuildableReference(
+                referencedContainer: "",
+                blueprint: PBXObject(),
+                buildableName: "",
+                blueprintName: ""
+            ),
+            skippedTests: [],
+            selectedTests: [],
+            useTestSelectionWhitelist: true
+        )
+        let subject = reference.xmlElement()
+        XCTAssertEqual(subject.attributes["skipped"], "NO")
+        XCTAssertEqual(subject.attributes["parallelizable"], "NO")
+        XCTAssertEqual(subject.attributes["useTestSelectionWhitelist"], "YES")
+        XCTAssertEqual(subject.attributes["testExecutionOrdering"], "random")
+    }
+
+    func test_write_testableReferenceAttributesValues_trueParallelizable() {
+        let reference = XCScheme.TestableReference(
+            skipped: false,
+            parallelizable: true,
+            randomExecutionOrdering: true,
+            buildableReference: XCScheme.BuildableReference(
+                referencedContainer: "",
+                blueprint: PBXObject(),
+                buildableName: "",
+                blueprintName: ""
+            ),
+            skippedTests: [],
+            selectedTests: [],
+            useTestSelectionWhitelist: true
+        )
+        let subject = reference.xmlElement()
+        XCTAssertEqual(subject.attributes["skipped"], "NO")
+        XCTAssertEqual(subject.attributes["parallelizable"], "YES")
+        XCTAssertEqual(subject.attributes["useTestSelectionWhitelist"], "YES")
+        XCTAssertEqual(subject.attributes["testExecutionOrdering"], "random")
+    }
+
+    func test_write_testableReferenceAttributesValues_falseParallelizable() {
+        let reference = XCScheme.TestableReference(
+            skipped: false,
+            parallelizable: false,
+            randomExecutionOrdering: true,
+            buildableReference: XCScheme.BuildableReference(
+                referencedContainer: "",
+                blueprint: PBXObject(),
+                buildableName: "",
+                blueprintName: ""
+            ),
+            skippedTests: [],
+            selectedTests: [],
+            useTestSelectionWhitelist: true
+        )
+        let subject = reference.xmlElement()
+        XCTAssertEqual(subject.attributes["skipped"], "NO")
+        XCTAssertEqual(subject.attributes["parallelizable"], "NO")
+        XCTAssertEqual(subject.attributes["useTestSelectionWhitelist"], "YES")
+        XCTAssertEqual(subject.attributes["testExecutionOrdering"], "random")
+    }
 
     func test_write_testableReferenceSelectedTests() {
         // Given