Issue 6090 - Allow use of console to be seen during tests

test/_common.js

Index: test/_common.js
===================================================================
--- a/test/_common.js
+++ b/test/_common.js
@@ -414,16 +414,35 @@
     Date: {
       now: () => currentTime
     }
   };
 };
 
 console.warn = console.log;
 
+exports.maybeExpectError = function(msg, test)

[sergei, 2017/11/24 10:15:28]

What about calling it `silenceAssertionOutput`?

[sergei, 2017/11/24 13:49:13]

JIC, I also thought that we could want to actually test that there is such
output from time to time by enabling an additional flag, and in this case
something like expectAssertionOutput would make sense, but I doubt that we
should really test assertion messages. We still can do it technically but
basically we want to deliberately not show expected messages.

[hub, 2017/11/24 15:48:59]

Done.

[hub, 2017/11/24 15:48:59]

I thought about expecting the output but then I'd need to check this is a DEBUG
build, otherwise assert2() is a noop.

+{
+  let msgMatch = new RegExp(`^Error: ${msg}[\r\n]`);
+  let errorHandler = globals.console.error;

[sergei, 2017/11/24 10:15:28]

I think it's OK taking into account that `console` is bound to `console.error`
and it's even in the same file.

[hub, 2017/11/24 15:48:59]

I'm missing a patch here where we actualle make console.log and console.error
work, I'll update with it.

+  globals.console.error = s =>
+  {
+    if (!msgMatch.test(s) && typeof errorHandler === "function")

[sergei, 2017/11/24 10:15:28]

I think we should not test the type of errorHandler because it would be better
to crash if it's not a function.

[hub, 2017/11/24 15:48:59]

Acknowledged.

+      errorHandler(s);
+  };
+  try
+  {
+    test();

[sergei, 2017/11/24 10:15:28]

IMO we should return the result of `test()` for the sake of simplicity.

[hub, 2017/11/24 15:48:59]

Acknowledged.

+  }
+  finally
+  {
+    globals.console.error = errorHandler;
+  }
+};
+
 exports.setupRandomResult = function()
 {
   let randomResult = 0.5;
   Object.defineProperty(this, "randomResult", {
     get: () => randomResult,
     set: value => randomResult = value
   });