Add self-verifying type-tracking tests.

Author: Max Schaefer

javascript/ql/test/library-tests/TypeTracking/TypeTracking.expected

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+| client2.js:3:6:3:16 | // track: f | Failed to track f here. |

javascript/ql/test/library-tests/TypeTracking/TypeTracking.ql

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+import javascript
+
+/** Gets a node to which the source node annotated with `name` is tracked under state `t`. */
+DataFlow::SourceNode trackNamedNode(DataFlow::TypeTracker t, string name) {
+  t.start() and
+  exists(Comment c, string f, int l |
+    f = c.getFile().getAbsolutePath() and
+    l = c.getLocation().getStartLine() and
+    result.hasLocationInfo(f, l, _, _, _) and
+    name = c.getText().regexpFind("(?<=name: )\\S+", _, _)
+  )
+  or
+  exists(DataFlow::TypeTracker t2 | result = trackNamedNode(t2, name).track(t2, t))
+}
+
+/** Holds if `name` is tracked to expression `e` starting on line `l` of file `f`. */
+predicate actual(Expr e, File f, int l, string name) {
+  trackNamedNode(DataFlow::TypeTracker::end(), name).flowsToExpr(e) and
+  f = e.getFile() and
+  l = e.getLocation().getStartLine()
+}
+
+/**
+ * Holds if there is an annotation comment expecting `name` to be tracked to an expression
+ * on line `l` of file `f`.
+ */
+predicate expected(Comment c, File f, int l, string name) {
+  f = c.getFile() and
+  l = c.getLocation().getStartLine() and
+  name = c.getText().regexpFind("(?<=track: )\\S+", _, _)
+}
+
+from Locatable loc, File f, int l, string name, string msg
+where
+  expected(loc, f, l, name) and
+  not actual(_, f, l, name) and
+  msg = "Failed to track " + name + " here."
+  or
+  actual(loc, f, l, name) and
+  not expected(_, f, l, name) and
+  expected(_, f, l, _) and
+  msg = "Unexpectedly tracked " + name + " here."
+select loc, msg

javascript/ql/test/library-tests/TypeTracking/client2.js

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+const g = require("./deprecated");
+
+g(); // track: f

javascript/ql/test/library-tests/TypeTracking/deprecated.js

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+const util = require("util");
+
+function f() {} // name: f
+
+module.exports = util.deprecate(f, "don't use this function");