diff --git a/cpp/ql/src/semmle/code/cpp/XML.qll b/cpp/ql/src/semmle/code/cpp/XML.qll
index 76e96fa1fc0a..21e48302788b 100644
--- a/cpp/ql/src/semmle/code/cpp/XML.qll
+++ b/cpp/ql/src/semmle/code/cpp/XML.qll
@@ -31,6 +31,12 @@ abstract class XMLLocatable extends @xmllocatable {
  * both of which can contain other elements.
  */
 class XMLParent extends @xmlparent {
+  XMLParent() {
+    // explicitly restrict `this` to be either an `XMLElement` or an `XMLFile`;
+    // the type `@xmlparent` currently also includes non-XML files
+    this instanceof @xmlelement or xmlEncoding(this, _)
+  }
+
   /**
    * Gets a printable representation of this XML parent.
    * (Intended to be overridden in subclasses.)
diff --git a/cpp/ql/test/library-tests/files/FilePath.expected b/cpp/ql/test/library-tests/files/FilePath.expected
deleted file mode 100644
index 6647c1e1fd7a..000000000000
--- a/cpp/ql/test/library-tests/files/FilePath.expected
+++ /dev/null
@@ -1,4 +0,0 @@
-| c.c | library-tests/files/c.c |
-| files1.cpp | library-tests/files/files1.cpp |
-| files1.h | library-tests/files/files1.h |
-| files2.cpp | library-tests/files/files2.cpp |
diff --git a/cpp/ql/test/library-tests/files/FilePath.ql b/cpp/ql/test/library-tests/files/FilePath.ql
deleted file mode 100644
index 724c4b45ae79..000000000000
--- a/cpp/ql/test/library-tests/files/FilePath.ql
+++ /dev/null
@@ -1,5 +0,0 @@
-import cpp
-
-from File f
-where f.toString() != ""
-select f.toString(), f.getRelativePath()
diff --git a/cpp/ql/test/library-tests/files/Files.expected b/cpp/ql/test/library-tests/files/Files.expected
new file mode 100644
index 000000000000..68187793433b
--- /dev/null
+++ b/cpp/ql/test/library-tests/files/Files.expected
@@ -0,0 +1,4 @@
+| c.c | library-tests/files/c.c | CFile, MetricFile | C |  |  |
+| files1.cpp | library-tests/files/files1.cpp | CppFile, MetricFile | C++ | swap | t |
+| files1.h | library-tests/files/files1.h | HeaderFile, MetricFile |  | swap |  |
+| files2.cpp | library-tests/files/files2.cpp | CppFile, MetricFile | C++ | g | x, y |
diff --git a/cpp/ql/test/library-tests/files/Files.ql b/cpp/ql/test/library-tests/files/Files.ql
new file mode 100644
index 000000000000..ee489c01843c
--- /dev/null
+++ b/cpp/ql/test/library-tests/files/Files.ql
@@ -0,0 +1,18 @@
+import cpp
+
+string describe(File f) {
+  f.compiledAsC() and
+  result = "C"
+  or
+  f.compiledAsCpp() and
+  result = "C++"
+  or
+  f instanceof XMLParent and
+  result = "XMLParent" // regression tests a bug in the characteristic predicate of XMLParent
+}
+
+from File f
+where f.toString() != ""
+select f.toString(), f.getRelativePath(), concat(f.getAQlClass().toString(), ", "),
+  concat(describe(f), ", "), concat(f.getATopLevelDeclaration().toString(), ", "),
+  concat(LocalVariable v | f.getADeclaration() = v | v.toString(), ", ")
diff --git a/cpp/ql/test/library-tests/files/Files1.expected b/cpp/ql/test/library-tests/files/Files1.expected
deleted file mode 100644
index ef11fb83e9be..000000000000
--- a/cpp/ql/test/library-tests/files/Files1.expected
+++ /dev/null
@@ -1 +0,0 @@
-| files1.h:0:0:0:0 | files1.h | files1.cpp:4:6:4:9 | swap |
diff --git a/cpp/ql/test/library-tests/files/Files1.ql b/cpp/ql/test/library-tests/files/Files1.ql
deleted file mode 100644
index a4db35de1b83..000000000000
--- a/cpp/ql/test/library-tests/files/Files1.ql
+++ /dev/null
@@ -1,4 +0,0 @@
-import cpp
-
-from HeaderFile f
-select f, f.getATopLevelDeclaration()
diff --git a/cpp/ql/test/library-tests/files/Files2.expected b/cpp/ql/test/library-tests/files/Files2.expected
deleted file mode 100644
index 7a2649c09e4a..000000000000
--- a/cpp/ql/test/library-tests/files/Files2.expected
+++ /dev/null
@@ -1,8 +0,0 @@
-| CFile      | C | --- | c.c |
-| CppFile    | - | C++ | files1.cpp |
-| CppFile    | - | C++ | files2.cpp |
-| HeaderFile | - | --- | files1.h |
-| MetricFile | - | --- | files1.h |
-| MetricFile | - | C++ | files1.cpp |
-| MetricFile | - | C++ | files2.cpp |
-| MetricFile | C | --- | c.c |
diff --git a/cpp/ql/test/library-tests/files/Files2.ql b/cpp/ql/test/library-tests/files/Files2.ql
deleted file mode 100644
index b87a06b97611..000000000000
--- a/cpp/ql/test/library-tests/files/Files2.ql
+++ /dev/null
@@ -1,11 +0,0 @@
-import cpp
-
-string isCompiledAsC(File f) { if f.compiledAsC() then result = "C" else result = "-" }
-
-string isCompiledAsCpp(File f) { if f.compiledAsCpp() then result = "C++" else result = "---" }
-
-from File f
-// On 64bit Linux, __va_list_tag is in the unknown file (""). Ignore it.
-where f.getAbsolutePath() != ""
-select (f.getAQlClass().toString() + "          ").prefix(10), isCompiledAsC(f), isCompiledAsCpp(f),
-  f.toString()
diff --git a/cpp/ql/test/library-tests/files/Files3.expected b/cpp/ql/test/library-tests/files/Files3.expected
deleted file mode 100644
index f17f4192871c..000000000000
--- a/cpp/ql/test/library-tests/files/Files3.expected
+++ /dev/null
@@ -1,3 +0,0 @@
-| files1.cpp | files1.cpp:4:6:4:9 | swap |
-| files1.h | files1.cpp:4:6:4:9 | swap |
-| files2.cpp | files2.cpp:3:6:3:6 | g |
diff --git a/cpp/ql/test/library-tests/files/Files3.ql b/cpp/ql/test/library-tests/files/Files3.ql
deleted file mode 100644
index 9d8d2ffc83c5..000000000000
--- a/cpp/ql/test/library-tests/files/Files3.ql
+++ /dev/null
@@ -1,7 +0,0 @@
-import cpp
-
-from File f, Declaration d
-where
-  d = f.getATopLevelDeclaration() and
-  d.getName() != "__va_list_tag"
-select f.toString(), d
diff --git a/cpp/ql/test/library-tests/files/Files4.expected b/cpp/ql/test/library-tests/files/Files4.expected
deleted file mode 100644
index 188b7161d991..000000000000
--- a/cpp/ql/test/library-tests/files/Files4.expected
+++ /dev/null
@@ -1,3 +0,0 @@
-| files1.cpp | files1.cpp:6:6:6:6 | t |
-| files2.cpp | files2.cpp:4:6:4:6 | x |
-| files2.cpp | files2.cpp:5:6:5:6 | y |
diff --git a/cpp/ql/test/library-tests/files/Files4.ql b/cpp/ql/test/library-tests/files/Files4.ql
deleted file mode 100644
index 104029795415..000000000000
--- a/cpp/ql/test/library-tests/files/Files4.ql
+++ /dev/null
@@ -1,5 +0,0 @@
-import cpp
-
-from File f, LocalVariable v
-where f.getADeclaration() = v
-select f.toString(), v