[Tests] NFC: Add a test-case for printing child notes associated with errors/warnings

Author: xedin

test/diagnostics/pretty-printed-diagnostics.swift

@@ -66,6 +66,9 @@ foo(b:
     1,
     a: 2)
 
+// Test for child notes attached directly to a "primary" error/warning diagnostic
+func test(a: Int) {}
+func test(a: Int) {}
 
 // Test fallback for non-ASCII characters.
 // CHECK: SOURCE_DIR{{[/\]+}}test{{[/\]+}}diagnostics{{[/\]+}}pretty-printed-diagnostics.swift:[[#LINE:]]:11
@@ -85,3 +88,9 @@ foo(b:
 // CHECK:  [[#LINE]] | foo(b: 1, a: 2)
 // CHECK:              |         `- error: argument 'a' must precede argument 'b'
 // CHECK: [[#LINE+1]]  |
+
+// CHECK: SOURCE_DIR{{[/\]+}}test{{[/\]+}}diagnostics{{[/\]+}}pretty-printed-diagnostics.swift:[[#LINE:]]:6
+// CHECK:  [[#LINE-1]] | func test(a: Int) {}
+// CHECK:              |      `- note: 'test(a:)' previously declared here
+// CHECK:  [[#LINE]]   |  func test(a: Int) {}
+// CHECL:  [[#LINE+1]] |       `- error: invalid redeclaration of 'test(a:)'