diff --git a/Sources/SourceKitLSP/TestDiscovery.swift b/Sources/SourceKitLSP/TestDiscovery.swift
index ef9ff3dc..2cdf638a 100644
--- a/Sources/SourceKitLSP/TestDiscovery.swift
+++ b/Sources/SourceKitLSP/TestDiscovery.swift
@@ -433,6 +433,7 @@ fileprivate extension Array<AnnotatedTestItem> {
   /// A node's parent is identified by the node's ID with the last component dropped.
   func mergingTestsInExtensions() -> [TestItem] {
     var itemDict: [String: AnnotatedTestItem] = [:]
+    var duplicatedIds: Set<String> = []
     for item in self {
       let id = item.testItem.id
       if var rootItem = itemDict[id] {
@@ -443,6 +444,10 @@ fileprivate extension Array<AnnotatedTestItem> {
           var newItem = item
           newItem.testItem.children += rootItem.testItem.children
           rootItem = newItem
+        } else if (rootItem.testItem.children.isEmpty && item.testItem.children.isEmpty) {
+          duplicatedIds.insert(item.testItem.id)
+          itemDict[item.testItem.fullyQualifiedTestId] = item
+          continue
         } else {
           rootItem.testItem.children += item.testItem.children
         }
@@ -475,10 +480,26 @@ fileprivate extension Array<AnnotatedTestItem> {
       .sorted { ($0.isExtension != $1.isExtension) ? !$0.isExtension : ($0.testItem.location < $1.testItem.location) }
 
     let result = sortedItems.map {
-      guard !$0.testItem.children.isEmpty, mergedIds.contains($0.testItem.id) else {
-        return $0.testItem
-      }
       var newItem = $0.testItem
+
+      // If multiple testItems share the same ID we add more context to make it unique.
+      // Two tests can share the same ID when two swift testing tests accept
+      // arguments of different types, i.e:
+      // @Test(arguments: [1,2,3]) func foo(_ x: Int) {}
+      // @Test(arguments: ["a", "b", "c"]) func foo(_ x: String) {}
+      // or when tests are in separate files but don't conflict because they are marked
+      // private, i.e:
+      // File1.swift: @Test private func foo() {}
+      // File2.swift: @Test private func foo() {}
+      // If we encounter one of these cases, we need to deduplicate the ID
+      // by appending /filename:filename:lineNumber.
+      if duplicatedIds.contains(newItem.id) {
+        newItem.id = newItem.fullyQualifiedTestId
+      }
+
+      guard !$0.testItem.children.isEmpty, mergedIds.contains($0.testItem.id) else {
+        return newItem
+      }
       newItem.children = newItem.children
         .map { AnnotatedTestItem(testItem: $0, isExtension: false) }
         .mergingTestsInExtensions()
@@ -498,6 +519,20 @@ fileprivate extension Array<AnnotatedTestItem> {
 }
 
 extension TestItem {
+  fileprivate var fullyQualifiedTestId: String {
+    return "\(self.id)/\(self.sourceLocation)"
+  }
+
+  private var sourceLocation: String {
+    let filename = self.location.uri.arbitrarySchemeURL.lastPathComponent
+    let position = location.range.lowerBound
+    // Lines and columns start at 1.
+    // swift-testing tests start from _after_ the @ symbol in @Test, so we need to add an extra column.
+    // see https://github.com/swiftlang/swift-testing/blob/cca6de2be617aded98ecdecb0b3b3a81eec013f3/Sources/TestingMacros/Support/AttributeDiscovery.swift#L153
+    let columnOffset = self.style == TestStyle.swiftTesting ? 2 : 1
+    return "\(filename):\(position.line + 1):\(position.utf16index + columnOffset)"
+  }
+
   fileprivate func prefixIDWithModuleName(workspace: Workspace) async -> TestItem {
     guard let canonicalTarget = await workspace.buildSystemManager.canonicalTarget(for: self.location.uri),
       let moduleName = await workspace.buildSystemManager.moduleName(for: self.location.uri, in: canonicalTarget)
diff --git a/Tests/SourceKitLSPTests/DocumentTestDiscoveryTests.swift b/Tests/SourceKitLSPTests/DocumentTestDiscoveryTests.swift
index 9f89290a..8ba285a8 100644
--- a/Tests/SourceKitLSPTests/DocumentTestDiscoveryTests.swift
+++ b/Tests/SourceKitLSPTests/DocumentTestDiscoveryTests.swift
@@ -418,6 +418,43 @@ final class DocumentTestDiscoveryTests: XCTestCase {
     )
   }
 
+  func testSwiftTestingTestsWithDuplicateFunctionIdentifiers() async throws {
+    let testClient = try await TestSourceKitLSPClient()
+    let uri = DocumentURI(for: .swift)
+
+    let positions = testClient.openDocument(
+      """
+      import Testing
+
+      1️⃣@Test(arguments: [1, 2, 3])
+      func foo(_ x: Int) {}2️⃣
+      3️⃣@Test(arguments: ["a", "b", "c"])
+      func foo(_ x: String) {}4️⃣
+      """,
+      uri: uri
+    )
+
+    let filename = uri.fileURL?.lastPathComponent ?? ""
+    let tests = try await testClient.send(DocumentTestsRequest(textDocument: TextDocumentIdentifier(uri)))
+    XCTAssertEqual(
+      tests,
+      [
+        TestItem(
+          id: "foo(_:)/\(filename):\(positions["1️⃣"].line + 1):\(positions["1️⃣"].utf16index + 2)",
+          label: "foo(_:)",
+          style: TestStyle.swiftTesting,
+          location: Location(uri: uri, range: positions["1️⃣"]..<positions["2️⃣"])
+        ),
+        TestItem(
+          id: "foo(_:)/\(filename):\(positions["3️⃣"].line + 1):\(positions["3️⃣"].utf16index + 2)",
+          label: "foo(_:)",
+          style: TestStyle.swiftTesting,
+          location: Location(uri: uri, range: positions["3️⃣"]..<positions["4️⃣"])
+        ),
+      ]
+    )
+  }
+
   func testSwiftTestingSuiteWithNoTests() async throws {
     let testClient = try await TestSourceKitLSPClient()
     let uri = DocumentURI(for: .swift)
diff --git a/Tests/SourceKitLSPTests/WorkspaceTestDiscoveryTests.swift b/Tests/SourceKitLSPTests/WorkspaceTestDiscoveryTests.swift
index 6126006f..0d1acbc9 100644
--- a/Tests/SourceKitLSPTests/WorkspaceTestDiscoveryTests.swift
+++ b/Tests/SourceKitLSPTests/WorkspaceTestDiscoveryTests.swift
@@ -245,6 +245,49 @@ final class WorkspaceTestDiscoveryTests: XCTestCase {
     )
   }
 
+  func testSwiftTestingTestsWithDuplicateFunctionIdentifiersAcrossDocuments() async throws {
+    let project = try await SwiftPMTestProject(
+      files: [
+        "Tests/MyLibraryTests/MyTests1.swift": """
+        import Testing
+
+        1️⃣@Test(arguments: [1, 2, 3])
+        private func foo(_ x: Int) {}2️⃣
+        """,
+        "Tests/MyLibraryTests/MyTests2.swift": """
+        import Testing
+
+        3️⃣@Test(arguments: [1, 2, 3])
+        private func foo(_ x: Int) {}4️⃣
+        """,
+      ],
+      manifest: packageManifestWithTestTarget
+    )
+
+    let test1Position = try project.position(of: "1️⃣", in: "MyTests1.swift")
+    let test2Position = try project.position(of: "3️⃣", in: "MyTests2.swift")
+
+    let tests = try await project.testClient.send(WorkspaceTestsRequest())
+
+    XCTAssertEqual(
+      tests,
+      [
+        TestItem(
+          id: "MyLibraryTests.foo(_:)/MyTests1.swift:\(test1Position.line + 1):\(test1Position.utf16index + 2)",
+          label: "foo(_:)",
+          style: TestStyle.swiftTesting,
+          location: try project.location(from: "1️⃣", to: "2️⃣", in: "MyTests1.swift")
+        ),
+        TestItem(
+          id: "MyLibraryTests.foo(_:)/MyTests2.swift:\(test2Position.line + 1):\(test2Position.utf16index + 2)",
+          label: "foo(_:)",
+          style: TestStyle.swiftTesting,
+          location: try project.location(from: "3️⃣", to: "4️⃣", in: "MyTests2.swift")
+        ),
+      ]
+    )
+  }
+
   func testSwiftTestingAndXCTestInTheSameFile() async throws {
     try SkipUnless.longTestsEnabled()