diff --git a/Tests/RunCMake/cmake_path/IS_PREFIX.cmake b/Tests/RunCMake/cmake_path/IS_PREFIX.cmake
index 9160dab11e..c4c6533105 100644
--- a/Tests/RunCMake/cmake_path/IS_PREFIX.cmake
+++ b/Tests/RunCMake/cmake_path/IS_PREFIX.cmake
@@ -24,4 +24,154 @@ if (NOT output)
   list (APPEND errors "'${path} is not prefix of '/a/c/../b'")
 endif()
 
+# The test is not strict: a path is a prefix of itself.
+set (prefix "/a/b")
+cmake_path(IS_PREFIX prefix "/a/b" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of '/a/b'")
+endif()
+
+# A trailing separator is an empty component, so it is significant on the
+# prefix, which then needs a further component to consume it.
+cmake_path(IS_PREFIX prefix "/a/b/" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of '/a/b/'")
+endif()
+set (prefix "/a/b/")
+cmake_path(IS_PREFIX prefix "/a/b" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of '/a/b'")
+endif()
+cmake_path(IS_PREFIX prefix "/a/b/c" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of '/a/b/c'")
+endif()
+
+# Without NORMALIZE, '.' and '..' are ordinary components, so a '..' escape
+# is still a lexical prefix and a '.' component defeats the match.
+set (prefix "/a/b")
+cmake_path(IS_PREFIX prefix "/a/b/../../etc" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of '/a/b/../../etc'")
+endif()
+cmake_path(IS_PREFIX prefix "/a/./b//c" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of '/a/./b//c'")
+endif()
+
+# Components are compared whole, so a sibling sharing a textual prefix does
+# not match.
+cmake_path(IS_PREFIX prefix "/a/bc" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of '/a/bc'")
+endif()
+
+# Relative paths are not made absolute, and the root directory is not an
+# exception to that rule.
+set (prefix "/a")
+cmake_path(IS_PREFIX prefix "b/c" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of 'b/c'")
+endif()
+set (prefix "b")
+cmake_path(IS_PREFIX prefix "b/c" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of 'b/c'")
+endif()
+set (prefix "/")
+cmake_path(IS_PREFIX prefix "b/c" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of 'b/c'")
+endif()
+cmake_path(IS_PREFIX prefix "/a/b" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of '/a/b'")
+endif()
+
+# A '.' prefix matches only a path that spells '.' too.
+set (prefix ".")
+cmake_path(IS_PREFIX prefix "a/b" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of 'a/b'")
+endif()
+cmake_path(IS_PREFIX prefix "./a/b" output)
+if (NOT output)
+  list (APPEND errors "'${prefix}' is not prefix of './a/b'")
+endif()
+
+# The empty path is a prefix of every path, including itself.
+set (prefix "")
+cmake_path(IS_PREFIX prefix "/a/b" output)
+if (NOT output)
+  list (APPEND errors "the empty path is not prefix of '/a/b'")
+endif()
+cmake_path(IS_PREFIX prefix "" output)
+if (NOT output)
+  list (APPEND errors "the empty path is not prefix of itself")
+endif()
+set (prefix "/a")
+cmake_path(IS_PREFIX prefix "" output)
+if (output)
+  list (APPEND errors "'${prefix}' is prefix of the empty path")
+endif()
+
+# Comparison follows the host path model.
+if(WIN32)
+  # Backslashes are separators, and are not converted.
+  set (prefix "C:\\a")
+  cmake_path(IS_PREFIX prefix "C:\\a\\b" output)
+  if (NOT output)
+    list (APPEND errors "'${prefix}' is not prefix of 'C:\\a\\b'")
+  endif()
+
+  # Comparison is case-sensitive even where the filesystem is not.  The
+  # second case isolates the root-name, since ordinary components are
+  # case-sensitive under every path model.
+  set (prefix "c:/a")
+  cmake_path(IS_PREFIX prefix "C:/A/b" output)
+  if (output)
+    list (APPEND errors "'${prefix}' is prefix of 'C:/A/b'")
+  endif()
+  cmake_path(IS_PREFIX prefix "C:/a/b" output)
+  if (output)
+    list (APPEND errors "'${prefix}' is prefix of 'C:/a/b'")
+  endif()
+
+  # A drive-relative path has a root-name but no root-directory, so it is
+  # relative and is not reconciled against an absolute prefix.
+  set (prefix "C:/")
+  cmake_path(IS_PREFIX prefix "C:foo" output)
+  if (output)
+    list (APPEND errors "'${prefix}' is prefix of 'C:foo'")
+  endif()
+else()
+  # Backslashes are ordinary filename characters.
+  set (prefix "C:\\a")
+  cmake_path(IS_PREFIX prefix "C:\\a\\b" output)
+  if (output)
+    list (APPEND errors "'${prefix}' is prefix of 'C:\\a\\b'")
+  endif()
+endif()
+
+if(WIN32 OR CYGWIN)
+  # '//host/share' is a root-name, not a doubled separator.
+  set (prefix "//host/share")
+  cmake_path(IS_PREFIX prefix "//host/share/a" output)
+  if (NOT output)
+    list (APPEND errors "'${prefix}' is not prefix of '//host/share/a'")
+  endif()
+  set (prefix "/a")
+  cmake_path(IS_PREFIX prefix "//a/b" output)
+  if (output)
+    list (APPEND errors "'${prefix}' is prefix of '//a/b'")
+  endif()
+else()
+  # A doubled leading separator collapses.
+  set (prefix "/a")
+  cmake_path(IS_PREFIX prefix "//a/b" output)
+  if (NOT output)
+    list (APPEND errors "'${prefix}' is not prefix of '//a/b'")
+  endif()
+endif()
+
 check_errors (IS_PREFIX ${errors})