Rename some variables in test case

Add one more test case to test the result of String.difference return sequential edits

Author: StevenWong12

Sources/_SwiftSyntaxTestSupport/SourceEditsTestUtils.swift

@@ -39,7 +39,11 @@ public func getConcurrentEdits(from base: String, to new: String) -> ConcurrentE
     }
 
   let sourceEdits = diffArray.map({
-    return $0.isInsert ? SourceEdit(offset: $0.offset, length: 0, replacementLength: 1) : SourceEdit(offset: $0.offset, length: 1, replacementLength: 0)
+    if $0.isInsert {
+      return SourceEdit(offset: $0.offset, length: 0, replacementLength: 1)
+    } else {
+      return SourceEdit(offset: $0.offset, length: 1, replacementLength: 0)
+    }
   })
 
   return ConcurrentEdits(fromSequential: sourceEdits)

Tests/SwiftParserTest/IncrementalParsingTests.swift

@@ -40,7 +40,7 @@ public class IncrementalParsingTests: XCTestCase {
 
     let newSource =
       """
-      struct A {}
+      struct AA {}
       struct B {}
       """
 

Tests/SwiftSyntaxTestSupportTest/SourceEditsTestUtilsTest.swift

@@ -15,29 +15,47 @@ import SwiftSyntax
 import _SwiftSyntaxTestSupport
 
 public class SourceEditsUtilTest: XCTestCase {
+  public func testStringDifferenceReturnSequentialEdits() {
+    let base = "0123"
+    let new = "a0123bc"
+
+    let diffs = getConcurrentEdits(from: base, to: new)
+    XCTAssertEqual(
+      diffs.edits,
+      [
+        SourceEdit(offset: 0, length: 0, replacementLength: 1),
+        SourceEdit(offset: 4, length: 0, replacementLength: 2),
+      ]
+    )
+
+    let appliedDiffsBase = applyEdits(diffs.edits, concurrent: true, to: base)
+
+    XCTAssertEqual(appliedDiffsBase, "?0123??")
+  }
+
   public func testDiffOfTwoStringsSimple() throws {
-    let s1 = "struct A { func f() {"
-    let s2 = "struct AA { func f() {"
+    let base = "struct A { func f() {"
+    let new = "struct AA { func f() {"
 
-    let diffs = getConcurrentEdits(from: s1, to: s2)
+    let diffs = getConcurrentEdits(from: base, to: new)
     XCTAssertEqual(diffs.edits.count, 1)
 
     let firstDiff = try XCTUnwrap(diffs.edits.first)
     XCTAssertEqual(firstDiff, SourceEdit(offset: 8, length: 0, replacementLength: 1))
   }
 
   public func testDiffOfTwoSameStrings() {
-    let s1 = "0123456"
+    let base = "0123456"
 
-    let diffs = getConcurrentEdits(from: s1, to: s1)
+    let diffs = getConcurrentEdits(from: base, to: base)
     XCTAssert(diffs.edits.isEmpty)
   }
 
   public func testDiffOfTwoStrings() {
-    let s1 = "0123456"
-    let s2 = "x12456yz"
+    let base = "0123456"
+    let new = "x12456yz"
 
-    let diffs = getConcurrentEdits(from: s1, to: s2)
+    let diffs = getConcurrentEdits(from: base, to: new)
 
     let expectedDiffs: [SourceEdit] = [
       SourceEdit(offset: 0, length: 1, replacementLength: 1),
@@ -47,8 +65,8 @@ public class SourceEditsUtilTest: XCTestCase {
 
     XCTAssertEqual(diffs.edits, expectedDiffs)
 
-    let s3 = applyEdits(expectedDiffs, concurrent: true, to: s1)
+    let appliedDiffsBase = applyEdits(expectedDiffs, concurrent: true, to: base)
 
-    XCTAssertEqual(s3, "?12456??")
+    XCTAssertEqual(appliedDiffsBase, "?12456??")
   }
 }