Tests: Fix tests for not auto-executing scripts without dataType

Two issues are fixed in testing for responses with a script Content-Type not
getting auto-executed unless an explicit `dataType: "script"` is provided:
* the test is now using a correct "text/javascript" Content-Type; it was using
  "text/html" until now which doesn't really check if the fix works
* the Node.js based version of the tests didn't account for an empty `header`
  query string parameter

Closes gh-4824
Ref gh-2432
Ref gh-2588
Ref 39cdb8c9aa0fde68f733553ba050a2ba9d86474c

(cherry picked from commit d38528b17a846b7ca4513b41150a05436546292d)

2 files changed, 2 insertions, 2 deletions

diff --git a/test/middleware-mockserver.js b/test/middleware-mockserver.js
index bb31eabfa..36216ecc1 100644
--- a/test/middleware-mockserver.js
+++ b/test/middleware-mockserver.js
@@ -62,7 +62,7 @@ var mocks = {
 	script: function( req, resp ) {
 		if ( req.query.header === "ecma" ) {
 			resp.writeHead( 200, { "content-type": "application/ecmascript" } );
-		} else if ( req.query.header ) {
+		} else if ( "header" in req.query ) {
 			resp.writeHead( 200, { "content-type": "text/javascript" } );
 		} else {
 			resp.writeHead( 200, { "content-type": "text/html" } );
diff --git a/test/unit/ajax.js b/test/unit/ajax.js
index 3f301f18f..bcb234640 100644
--- a/test/unit/ajax.js
+++ b/test/unit/ajax.js
@@ -114,7 +114,7 @@ QUnit.module( "ajax", {
 		return {
 			create: function( options ) {
 				options.crossDomain = true;
-				return jQuery.ajax( url( "mock.php?action=script" ), options );
+				return jQuery.ajax( url( "mock.php?action=script&header" ), options );
 			},
 			success: function() {
 				assert.ok( true, "success" );