docs for assert.throws

doc/api/assert.markdown

@@ -37,11 +37,44 @@ Tests strict non-equality, as determined by the strict not equal operator ( `!==
 
 ### assert.throws(block, [error], [message])
 
-Expects `block` to throw an error.
+Expects `block` to throw an error. `error` can be constructor, regexp or 
+validation function.
+
+Validate instanceof using constructor:
+
+    assert.throws(
+      function() {
+        throw new Error("Wrong value");
+      },
+      Error
+    );
+
+Validate error message using RegExp:
+
+    assert.throws(
+      function() {
+        throw new Error("Wrong value");
+      },
+      /value/
+    );
+
+Custom error validation:
+
+    assert.throws(
+      function() {
+        throw new Error("Wrong value");
+      },
+      function(err) {
+        if ( !(err instanceof Error) || !/value/.test(err) ) {
+          return false;
+        }
+      },
+      "unexpected error"
+    );
 
 ### assert.doesNotThrow(block, [error], [message])
 
-Expects `block` not to throw an error.
+Expects `block` not to throw an error, see assert.throws for details.
 
 ### assert.ifError(value)