Documented the String+Constants extension in the library target.

Test/Sources/Cases/Internal/Enumerations/IndexPrefixTests.swift

@@ -5,6 +5,8 @@ import Testing
 @Suite("IndexPrefix", .tags(.enumeration))
 struct IndexPrefixTests {
 
+    // MARK: Properties tests
+
     @Test(arguments: zip(IndexPrefix.allCases, [String].paths))
     func path(
         for prefix: IndexPrefix,

Test/Sources/Cases/Internal/Enumerations/StaticFileTests.swift

@@ -5,6 +5,8 @@ import Testing
 @Suite("StaticFile", .tags(.enumeration))
 struct StaticFileTests {
 
+    // MARK: Properties tests
+
     @Test(arguments: zip(StaticFile.allCases, [String].paths))
     func path(
         for prefix: StaticFile,