diff --git a/Sources/SwiftSyntaxMacrosTestSupport/Assertions.swift b/Sources/SwiftSyntaxMacrosTestSupport/Assertions.swift
index 5a3fcdbd2c8..167900d68e0 100644
--- a/Sources/SwiftSyntaxMacrosTestSupport/Assertions.swift
+++ b/Sources/SwiftSyntaxMacrosTestSupport/Assertions.swift
@@ -34,8 +34,10 @@ public struct NoteSpec {
   public let column: Int
 
   /// The file and line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
-  internal let originatorFile: StaticString
+  internal let originatorFileID: String
+  internal let originatorFilePath: StaticString
   internal let originatorLine: UInt
+  internal let originatorColumn: UInt
 
   /// Creates a new ``NoteSpec`` that describes a note tests are expecting to be generated by a macro expansion.
   ///
@@ -43,32 +45,65 @@ public struct NoteSpec {
   ///   - message: The expected message of the note
   ///   - line: The line to which the note is expected to point
   ///   - column: The column to which the note is expected to point
-  ///   - originatorFile: The file at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFileID: The file ID at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFilePath: The file path at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   ///   - originatorLine: The line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorColumn: The column at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   public init(
     message: String,
     line: Int,
     column: Int,
-    originatorFile: StaticString = #file,
-    originatorLine: UInt = #line
+    originatorFileID: String = #fileID,
+    originatorFilePath: StaticString = #filePath,
+    originatorLine: UInt = #line,
+    originatorColumn: UInt = #column
   ) {
     self.message = message
     self.line = line
     self.column = column
-    self.originatorFile = originatorFile
+    self.originatorFileID = originatorFileID
+    self.originatorFilePath = originatorFilePath
     self.originatorLine = originatorLine
+    self.originatorColumn = originatorColumn
   }
 }
 
 func assertNote(
   _ note: Note,
   in expansionContext: BasicMacroExpansionContext,
-  expected spec: NoteSpec
+  expected spec: NoteSpec,
+  failingWith failureHandler: ((_ message: String, _ fileID: String, _ filePath: StaticString, _ line: UInt, _ column: UInt) -> Void)? = nil
 ) {
-  assertStringsEqualWithDiff(note.message, spec.message, "message of note does not match", file: spec.originatorFile, line: spec.originatorLine)
+  let failureHandler = failureHandler ?? defaultFailureHandler
+  if note.message != spec.message {
+    let message = describeDifferenceBetweenStrings(note.message, spec.message, "message of note does not match")
+    failureHandler(
+      message,
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
   let location = expansionContext.location(for: note.position, anchoredAt: note.node, fileName: "")
-  XCTAssertEqual(location.line, spec.line, "line of note does not match", file: spec.originatorFile, line: spec.originatorLine)
-  XCTAssertEqual(location.column, spec.column, "column of note does not match", file: spec.originatorFile, line: spec.originatorLine)
+  if location.line != spec.line {
+    failureHandler(
+      "line \(location.line) of note does not match \(spec.line)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
+  if location.column != spec.column {
+    failureHandler(
+      "column \(location.column) of note does not match \(spec.column)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
 }
 
 // MARK: - Fix-It
@@ -82,31 +117,50 @@ public struct FixItSpec {
   public let message: String
 
   /// The file and line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
-  internal let originatorFile: StaticString
+  internal let originatorFileID: String
+  internal let originatorFilePath: StaticString
   internal let originatorLine: UInt
+  internal let originatorColumn: UInt
 
   /// Creates a new ``FixItSpec`` that describes a Fix-It tests are expecting to be generated by a macro expansion.
   ///
   /// - Parameters:
   ///   - message: The expected message of the note
-  ///   - originatorFile: The file at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFileID: The file ID at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFilePath: The file path at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   ///   - originatorLine: The line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorColumn: The column at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   public init(
     message: String,
-    originatorFile: StaticString = #file,
-    originatorLine: UInt = #line
+    originatorFileID: String = #fileID,
+    originatorFilePath: StaticString = #filePath,
+    originatorLine: UInt = #line,
+    originatorColumn: UInt = #column
   ) {
     self.message = message
-    self.originatorFile = originatorFile
+    self.originatorFileID = originatorFileID
+    self.originatorFilePath = originatorFilePath
     self.originatorLine = originatorLine
+    self.originatorColumn = originatorColumn
   }
 }
 
 func assertFixIt(
   _ fixIt: FixIt,
-  expected spec: FixItSpec
+  expected spec: FixItSpec,
+  failingWith failureHandler: ((_ message: String, _ fileID: String, _ filePath: StaticString, _ line: UInt, _ column: UInt) -> Void)? = nil
 ) {
-  assertStringsEqualWithDiff(fixIt.message.message, spec.message, "message of Fix-It does not match", file: spec.originatorFile, line: spec.originatorLine)
+  let failureHandler = failureHandler ?? defaultFailureHandler
+  if fixIt.message.message != spec.message {
+    let message = describeDifferenceBetweenStrings(fixIt.message.message, spec.message, "message of Fix-It does not match")
+    failureHandler(
+      message,
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
 }
 
 // MARK: - Diagnostic
@@ -138,8 +192,10 @@ public struct DiagnosticSpec {
   public let fixIts: [FixItSpec]
 
   /// The file and line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
-  internal let originatorFile: StaticString
+  internal let originatorFileID: String
+  internal let originatorFilePath: StaticString
   internal let originatorLine: UInt
+  internal let originatorColumn: UInt
 
   /// Creates a new ``DiagnosticSpec`` that describes a diagnostic tests are expecting to be generated by a macro expansion.
   ///
@@ -152,8 +208,10 @@ public struct DiagnosticSpec {
   ///   - highlights: If not empty, the text fragments the diagnostic is expected to highlight
   ///   - notes: The notes that are expected to be attached to the diagnostic
   ///   - fixIts: The messages of the Fix-Its the diagnostic is expected to produce
-  ///   - originatorFile: The file at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFileID: The file ID at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorFilePath: The file path at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   ///   - originatorLine: The line at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
+  ///   - originatorColumn: The column at which this ``NoteSpec`` was created, so that assertion failures can be reported at its location.
   public init(
     id: MessageID? = nil,
     message: String,
@@ -163,8 +221,10 @@ public struct DiagnosticSpec {
     highlights: [String]? = nil,
     notes: [NoteSpec] = [],
     fixIts: [FixItSpec] = [],
-    originatorFile: StaticString = #file,
-    originatorLine: UInt = #line
+    originatorFileID: String = #fileID,
+    originatorFilePath: StaticString = #filePath,
+    originatorLine: UInt = #line,
+    originatorColumn: UInt = #column
   ) {
     self.id = id
     self.message = message
@@ -174,8 +234,10 @@ public struct DiagnosticSpec {
     self.highlights = highlights
     self.notes = notes
     self.fixIts = fixIts
-    self.originatorFile = originatorFile
+    self.originatorFileID = originatorFileID
+    self.originatorFilePath = originatorFilePath
     self.originatorLine = originatorLine
+    self.originatorColumn = originatorColumn
   }
 }
 
@@ -189,7 +251,7 @@ extension DiagnosticSpec {
   }
 
   @_disfavoredOverload
-  @available(*, deprecated, message: "Use init(id:message:line:column:severity:highlights:notes:fixIts:originatorFile:originatorLine:) instead")
+  @available(*, deprecated, message: "Use init(id:message:line:column:severity:highlights:notes:fixIts:originatorFileID:originatorFilePath:originatorLine:originatorColumn:) instead")
   public init(
     id: MessageID? = nil,
     message: String,
@@ -218,70 +280,132 @@ extension DiagnosticSpec {
 func assertDiagnostic(
   _ diag: Diagnostic,
   in expansionContext: BasicMacroExpansionContext,
-  expected spec: DiagnosticSpec
+  expected spec: DiagnosticSpec,
+  failingWith failureHandler: ((_ message: String, _ fileID: String, _ filePath: StaticString, _ line: UInt, _ column: UInt) -> Void)? = nil
 ) {
-  if let id = spec.id {
-    XCTAssertEqual(diag.diagnosticID, id, "diagnostic ID does not match", file: spec.originatorFile, line: spec.originatorLine)
+  let failureHandler = failureHandler ?? defaultFailureHandler
+
+  if let id = spec.id, diag.diagnosticID != id {
+    failureHandler(
+      "diagnostic ID \(diag.diagnosticID) does not match \(id)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
+  if diag.message != spec.message {
+    let message = describeDifferenceBetweenStrings(diag.message, spec.message, "message does not match")
+    failureHandler(
+      message,
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
   }
-  assertStringsEqualWithDiff(diag.message, spec.message, "message does not match", file: spec.originatorFile, line: spec.originatorLine)
   let location = expansionContext.location(for: diag.position, anchoredAt: diag.node, fileName: "")
-  XCTAssertEqual(location.line, spec.line, "line does not match", file: spec.originatorFile, line: spec.originatorLine)
-  XCTAssertEqual(location.column, spec.column, "column does not match", file: spec.originatorFile, line: spec.originatorLine)
-
-  XCTAssertEqual(spec.severity, diag.diagMessage.severity, "severity does not match", file: spec.originatorFile, line: spec.originatorLine)
+  if location.line != spec.line {
+    failureHandler(
+      "line \(location.line) does not match \(spec.line)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
+  if location.column != spec.column {
+    failureHandler(
+      "column \(location.column) does not match \(spec.column)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
+  if spec.severity != diag.diagMessage.severity {
+    failureHandler(
+      "severity \(spec.severity) does not match \(diag.diagMessage.severity)",
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
+    )
+  }
 
   if let highlights = spec.highlights {
     if diag.highlights.count != highlights.count {
-      XCTFail(
+      failureHandler(
         """
         Expected \(highlights.count) highlights but received \(diag.highlights.count):
         \(diag.highlights.map(\.trimmedDescription).joined(separator: "\n"))
         """,
-        file: spec.originatorFile,
-        line: spec.originatorLine
+        spec.originatorFileID,
+        spec.originatorFilePath,
+        spec.originatorLine,
+        spec.originatorColumn
       )
     } else {
-      for (actual, expected) in zip(diag.highlights, highlights) {
-        assertStringsEqualWithDiff(
-          actual.trimmedDescription,
-          expected,
-          "highlight does not match",
-          file: spec.originatorFile,
-          line: spec.originatorLine
-        )
+      for (actual, expected) in zip(diag.highlights.lazy.map(\.trimmedDescription), highlights) {
+        if actual != expected {
+          let message = describeDifferenceBetweenStrings(actual, expected, "highlight does not match")
+          failureHandler(
+            message,
+            spec.originatorFileID,
+            spec.originatorFilePath,
+            spec.originatorLine,
+            spec.originatorColumn
+          )
+        }
       }
     }
   }
   if diag.notes.count != spec.notes.count {
-    XCTFail(
+    failureHandler(
       """
       Expected \(spec.notes.count) notes but received \(diag.notes.count):
       \(diag.notes.map(\.debugDescription).joined(separator: "\n"))
       """,
-      file: spec.originatorFile,
-      line: spec.originatorLine
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
     )
   } else {
     for (note, expectedNote) in zip(diag.notes, spec.notes) {
-      assertNote(note, in: expansionContext, expected: expectedNote)
+      assertNote(note, in: expansionContext, expected: expectedNote, failingWith: failureHandler)
     }
   }
   if diag.fixIts.count != spec.fixIts.count {
-    XCTFail(
+    failureHandler(
       """
       Expected \(spec.fixIts.count) Fix-Its but received \(diag.fixIts.count):
       \(diag.fixIts.map(\.message.message).joined(separator: "\n"))
       """,
-      file: spec.originatorFile,
-      line: spec.originatorLine
+      spec.originatorFileID,
+      spec.originatorFilePath,
+      spec.originatorLine,
+      spec.originatorColumn
     )
   } else {
     for (fixIt, expectedFixIt) in zip(diag.fixIts, spec.fixIts) {
-      assertFixIt(fixIt, expected: expectedFixIt)
+      assertFixIt(fixIt, expected: expectedFixIt, failingWith: failureHandler)
     }
   }
 }
 
+private func defaultFailureHandler(
+  _ message: String,
+  fileID: String = #fileID,
+  filePath: StaticString = #filePath,
+  line: UInt = #line,
+  column: UInt = #column
+) {
+  // FIXME: detect if XCTest is currently running a test and only call XCTFail() if it is.
+  // FIXME: support swift-testing.
+  XCTFail(message, file: filePath, line: line)
+}
+
 /// Assert that expanding the given macros in the original source produces
 /// the given expanded source code.
 ///
@@ -299,6 +423,7 @@ func assertDiagnostic(
 ///   - testModuleName: The name of the test module to use.
 ///   - testFileName: The name of the test file name to use.
 ///   - indentationWidth: The indentation width used in the expansion.
+///   - failureHandler: A closure to call if the assertion fails. This closure may be called more than once. If `nil`, `XCTFail()` is called.
 public func assertMacroExpansion(
   _ originalSource: String,
   expandedSource expectedExpandedSource: String,
@@ -309,9 +434,14 @@ public func assertMacroExpansion(
   testModuleName: String = "TestModule",
   testFileName: String = "test.swift",
   indentationWidth: Trivia = .spaces(4),
-  file: StaticString = #file,
-  line: UInt = #line
+  failingWith failureHandler: ((_ message: String, _ fileID: String, _ filePath: StaticString, _ line: UInt, _ column: UInt) -> Void)? = nil,
+  fileID: String = #fileID,
+  filePath: StaticString = #filePath,
+  line: UInt = #line,
+  column: UInt = #column
 ) {
+  let failureHandler = failureHandler ?? defaultFailureHandler
+
   // Parse the original source file.
   let origSourceFile = Parser.parse(source: originalSource)
 
@@ -323,7 +453,7 @@ public func assertMacroExpansion(
   let expandedSourceFile = origSourceFile.expand(macros: macros, in: context, indentationWidth: indentationWidth)
   let diags = ParseDiagnosticsGenerator.diagnostics(for: expandedSourceFile)
   if !diags.isEmpty {
-    XCTFail(
+    failureHandler(
       """
       Expanded source should not contain any syntax errors, but contains:
       \(DiagnosticsFormatter.annotatedSource(tree: expandedSourceFile, diags: diags))
@@ -331,35 +461,44 @@ public func assertMacroExpansion(
       Expanded syntax tree was:
       \(expandedSourceFile.debugDescription)
       """,
-      file: file,
-      line: line
+      fileID,
+      filePath,
+      line,
+      column
     )
   }
 
-  assertStringsEqualWithDiff(
-    expandedSourceFile.description.trimmingCharacters(in: .newlines),
-    expectedExpandedSource.trimmingCharacters(in: .newlines),
-    "Macro expansion did not produce the expected expanded source",
-    additionalInfo: """
-      Actual expanded source:
-      \(expandedSourceFile)
-      """,
-    file: file,
-    line: line
-  )
+  do {
+    let expandedSourceFile = expandedSourceFile.description.trimmingCharacters(in: .newlines)
+    let expectedExpandedSource = expectedExpandedSource.trimmingCharacters(in: .newlines)
+    if expandedSourceFile != expectedExpandedSource {
+      let message = describeDifferenceBetweenStrings(
+        expandedSourceFile,
+        expectedExpandedSource,
+        "Macro expansion did not produce the expected expanded source",
+        additionalInfo: """
+          Actual expanded source:
+          \(expandedSourceFile)
+          """
+      )
+      failureHandler(message, fileID, filePath, line, column)
+    }
+  }
 
   if context.diagnostics.count != diagnostics.count {
-    XCTFail(
+    failureHandler(
       """
       Expected \(diagnostics.count) diagnostics but received \(context.diagnostics.count):
       \(context.diagnostics.map(\.debugDescription).joined(separator: "\n"))
       """,
-      file: file,
-      line: line
+      fileID,
+      filePath,
+      line,
+      column
     )
   } else {
     for (actualDiag, expectedDiag) in zip(context.diagnostics, diagnostics) {
-      assertDiagnostic(actualDiag, in: context, expected: expectedDiag)
+      assertDiagnostic(actualDiag, in: context, expected: expectedDiag, failingWith: failureHandler)
     }
   }
 
@@ -376,12 +515,14 @@ public func assertMacroExpansion(
 
     let fixedTree = FixItApplier.apply(edits: edits, to: origSourceFile)
     let fixedTreeDescription = fixedTree.description
-    assertStringsEqualWithDiff(
-      fixedTreeDescription.trimmingTrailingWhitespace(),
-      expectedFixedSource.trimmingTrailingWhitespace(),
-      file: file,
-      line: line
-    )
+    do {
+      let fixedTreeDescription = fixedTreeDescription.trimmingTrailingWhitespace()
+      let expectedFixedSource = expectedFixedSource.trimmingTrailingWhitespace()
+      if fixedTreeDescription != expectedFixedSource {
+        let message = describeDifferenceBetweenStrings(fixedTreeDescription, expectedFixedSource)
+        failureHandler(message, fileID, filePath, line, column)
+      }
+    }
   }
 }
 
diff --git a/Sources/_SwiftSyntaxTestSupport/AssertEqualWithDiff.swift b/Sources/_SwiftSyntaxTestSupport/AssertEqualWithDiff.swift
index f230e86690a..6b81fd41498 100644
--- a/Sources/_SwiftSyntaxTestSupport/AssertEqualWithDiff.swift
+++ b/Sources/_SwiftSyntaxTestSupport/AssertEqualWithDiff.swift
@@ -88,6 +88,16 @@ public func failStringsEqualWithDiff(
   file: StaticString = #file,
   line: UInt = #line
 ) {
+  let fullMessage = describeDifferenceBetweenStrings(actual, expected, message, additionalInfo: additionalInfo())
+  XCTFail(fullMessage, file: file, line: line)
+}
+
+public func describeDifferenceBetweenStrings(
+  _ actual: String,
+  _ expected: String,
+  _ message: String = "",
+  additionalInfo: @autoclosure () -> String? = nil
+) -> String {
   let stringComparison: String
 
   // Use `CollectionDifference` on supported platforms to get `diff`-like line-based output. On
@@ -151,5 +161,5 @@ public func failStringsEqualWithDiff(
       \(additional)
       """
   }
-  XCTFail(fullMessage, file: file, line: line)
+  return fullMessage
 }