Add test case

Author: kitasuke

Tests/SwiftSyntaxTest/SyntaxFactory.swift

@@ -24,6 +24,7 @@ public class SyntaxFactoryAPITestCase: XCTestCase {
     ("testFunctionCallSyntaxBuilder", testFunctionCallSyntaxBuilder),
     ("testWithOptionalChild", testWithOptionalChild),
     ("testUnknownSyntax", testUnknownSyntax),
+    ("testMakeStringLiteralExpr", testMakeStringLiteralExpr),
   ]
 
   public func testGenerated() {
@@ -160,4 +161,16 @@ public class SyntaxFactoryAPITestCase: XCTestCase {
     XCTAssertNoThrow(try SyntaxVerifier.verify(expr))
     XCTAssertThrowsError(try SyntaxVerifier.verify(unknown))
   }
+
+  public func testMakeStringLiteralExpr() {
+    let expr = SyntaxFactory.makeStringLiteralExpr(
+      "Hello, world!",
+      leadingTrivia: .init(pieces: [.lineComment("// hello"), .newlines(1)])
+    )
+    let expected = """
+// hello
+"Hello, world!"
+"""
+    XCTAssertEqual(expr.description, expected)
+  }
 }