add tests

tests/stdlib/tassertions.nim

@@ -0,0 +1,29 @@
+discard """
+targets: "c cpp js"
+"""
+
+template main =
+  doAssertRaises(ValueError): raise newException(ValueError, "foo")
+  doAssertRaises(ValueError, block: raise newException(ValueError, "foo"))
+static: main()
+main()
+
+when defined(cpp) or defined(js):
+  when defined(cpp):
+    {.emit:"""
+    #include <stdexcept>
+    void fn(){throw std::runtime_error("asdf");}""".}
+    proc fn(){.importcpp.}
+  else:
+    {.emit:"""
+    function fn(){ throw 42;} """.}
+    proc fn(){.importc.}
+
+  var witness = false
+  try:
+    doAssertRaises(ValueError): fn()
+  except AssertionDefect:
+    witness = true
+  doAssert witness
+  doAssertRaises: fn()
+  doAssertRaises(block: fn())