feat: include .cause stacks in the error stack traces

lib/reporters/base.js

@@ -221,6 +221,56 @@ var generateDiff = (exports.generateDiff = function (actual, expected) {
   }
 });
 
+/**
+ * Traverses err.cause and returns all stack traces
+ *
+ * @private
+ * @param {Error} err
+ * @param {Set<Error>} [seen]
+ * @return {{ message: string, msg: string, stack: string }}
+ */
+var getFullErrorStack = function (err, seen) {
+  if (seen && seen.has(err)) {
+    return { message: '', msg: '<circular>', stack: '' };
+  }
+
+  var message;
+
+  if (typeof err.inspect === 'function') {
+    message = err.inspect() + '';
+  } else if (err.message && typeof err.message.toString === 'function') {
+    message = err.message + '';
+  } else {
+    message = '';
+  }
+
+  var msg;
+  var stack = err.stack || message;
+  var index = message ? stack.indexOf(message) : -1;
+
+  if (index === -1) {
+    msg = message;
+  } else {
+    index += message.length;
+    msg = stack.slice(0, index);
+    // remove msg from stack
+    stack = stack.slice(index + 1);
+
+    if (err.cause) {
+      seen = seen || new Set();
+      seen.add(err);
+      const causeStack = getFullErrorStack(err.cause, seen)
+      stack += '\n   Caused by: ' + causeStack.msg + (causeStack.stack ? '\n' + causeStack.stack : '');
+    }
+  }
+
+  return {
+    message,
+    msg,
+    stack
+  };
+};
+
 /**
  * Outputs the given `failures` as a list.
  *
@@ -241,7 +291,6 @@ exports.list = function (failures) {
       color('error stack', '\n%s\n');
 
     // msg
-    var msg;
     var err;
     if (test.err && test.err.multiple) {
       if (multipleTest !== test) {
@@ -252,25 +301,8 @@ exports.list = function (failures) {
     } else {
       err = test.err;
     }
-    var message;
-    if (typeof err.inspect === 'function') {
-      message = err.inspect() + '';
-    } else if (err.message && typeof err.message.toString === 'function') {
-      message = err.message + '';
-    } else {
-      message = '';
-    }
-    var stack = err.stack || message;
-    var index = message ? stack.indexOf(message) : -1;
 
-    if (index === -1) {
-      msg = message;
-    } else {
-      index += message.length;
-      msg = stack.slice(0, index);
-      // remove msg from stack
-      stack = stack.slice(index + 1);
-    }
+    var { message, msg, stack } = getFullErrorStack(err);
 
     // uncaught
     if (err.uncaught) {

lib/runner.js

@@ -443,11 +443,22 @@ Runner.prototype.fail = function (test, err, force) {
     err = thrown2Error(err);
   }
 
-  try {
-    err.stack =
-      this.fullStackTrace || !err.stack ? err.stack : stackFilter(err.stack);
-  } catch (ignore) {
-    // some environments do not take kindly to monkeying with the stack
+  // Filter the stack traces
+  if (!this.fullStackTrace) {
+    const alreadyFiltered = new Set();
+    let currentErr = err;
+
+    while (currentErr && currentErr.stack && !alreadyFiltered.has(currentErr)) {
+      alreadyFiltered.add(currentErr);
+
+      try {
+        currentErr.stack = stackFilter(currentErr.stack);
+      } catch (ignore) {
+        // some environments do not take kindly to monkeying with the stack
+      }
+
+      currentErr = currentErr.cause;
+    }
   }
 
   this.emit(constants.EVENT_TEST_FAIL, test, err);

test/reporters/base.spec.js

@@ -491,6 +491,108 @@ describe('Base reporter', function () {
     expect(errOut, 'to be', '1) test title:\n     Error\n  foo\n  bar');
   });
 
+  describe('error causes', function () {
+    it('should append any error cause trail to stack traces', function () {
+      var err = {
+        message: 'Error',
+        stack: 'Error\nfoo\nbar',
+        showDiff: false,
+        cause: {
+          message: 'Cause1',
+          stack: 'Cause1\nbar\nfoo',
+          showDiff: false,
+          cause: {
+            message: 'Cause2',
+            stack: 'Cause2\nabc\nxyz',
+            showDiff: false
+          }
+        }
+      };
+      var test = makeTest(err);
+
+      list([test]);
+
+      var errOut = stdout.join('\n').trim();
+      expect(
+        errOut,
+        'to be',
+        '1) test title:\n     Error\n  foo\n  bar\n     Caused by: Cause1\n  bar\n  foo\n     Caused by: Cause2\n  abc\n  xyz'
+      );
+    });
+
+    it('should not get stuck in a hypothetical circular error cause trail', function () {
+      var err1 = {
+        message: 'Error',
+        stack: 'Error\nfoo\nbar',
+        showDiff: false,
+      };
+      var err2 = {
+        message: 'Cause1',
+        stack: 'Cause1\nbar\nfoo',
+        showDiff: false,
+        cause: err1
+      }
+      err1.cause = err2;
+
+      var test = makeTest(err1);
+
+      list([test]);
+
+      var errOut = stdout.join('\n').trim();
+      expect(
+        errOut,
+        'to be',
+        '1) test title:\n     Error\n  foo\n  bar\n     Caused by: Cause1\n  bar\n  foo\n     Caused by: <circular>'
+      );
+    });
+
+    it("should set an empty cause if neither 'inspect' nor 'message' is set", function () {
+      var err = {
+        message: 'Error',
+        stack: 'Error\nfoo\nbar',
+        showDiff: false,
+        cause: {
+          showDiff: false,
+        }
+      };
+
+      var test = makeTest(err);
+
+      list([test]);
+
+      var errOut = stdout.join('\n').trim();
+      expect(
+        errOut,
+        'to be',
+        '1) test title:\n     Error\n  foo\n  bar\n     Caused by:'
+      );
+    });
+
+    it('should not add cause trail if error does not contain message', function () {
+      var err = {
+        message: 'Error',
+        stack: 'foo\nbar',
+        showDiff: false,
+        cause: {
+          message: 'Cause1',
+          stack: 'Cause1\nbar\nfoo',
+          showDiff: false,
+          cause: {
+            message: 'Cause2',
+            stack: 'Cause2\nabc\nxyz',
+            showDiff: false
+          }
+        }
+      };
+      var test = makeTest(err);
+
+      list([test]);
+
+      var errOut = stdout.join('\n').trim();
+      expect(errOut, 'to be', '1) test title:\n     Error\n  foo\n  bar');
+    });
+  });
+
   it('should list multiple Errors per test', function () {
     var err = new Error('First Error');
     err.multiple = [new Error('Second Error - same test')];

test/unit/runner.spec.js

@@ -629,6 +629,22 @@ describe('Runner', function () {
             });
             runner.fail(hook, err);
           });
+
+          it('should prettify stack-traces in error cause trail', function (done) {
+            var hook = new Hook();
+            hook.parent = suite;
+            var causeErr = new Error();
+            // Fake stack-trace
+            causeErr.stack = stack.join('\n');
+            var err = new Error();
+            err.cause = causeErr;
+
+            runner.on(EVENT_TEST_FAIL, function (_hook, _err) {
+              expect(_err.cause.stack, 'to be', stack.slice(0, 3).join('\n'));
+              done();
+            });
+            runner.fail(hook, err);
+          });
         });
 
         describe('long', function () {
@@ -647,6 +663,24 @@ describe('Runner', function () {
             });
             runner.fail(hook, err);
           });
+
+          it('should display full stack-traces in error cause trail', function (done) {
+            var hook = new Hook();
+            hook.parent = suite;
+            var causeErr = new Error();
+            // Fake stack-trace
+            causeErr.stack = stack.join('\n');
+            var err = new Error();
+            err.cause = causeErr;
+            // Add --stack-trace option
+            runner.fullStackTrace = true;
+
+            runner.on(EVENT_TEST_FAIL, function (_hook, _err) {
+              expect(_err.cause.stack, 'to be', stack.join('\n'));
+              done();
+            });
+            runner.fail(hook, err);
+          });
         });
 
         describe('ginormous', function () {