[Fix] fix stack where actual is falsy

Fixes tape-testing#399.

Author: nhamer

lib/results.js

@@ -157,7 +157,7 @@ function encodeResult (res, count) {
         output += inner + 'at: ' + res.at + '\n';
     }
 
-    var actualStack = res.actual && res.actual.stack;
+    var actualStack = res.actual && (typeof res.actual === 'object' || typeof res.actual === 'function') ? res.actual.stack : undefined;
     var errorStack = res.error && res.error.stack;
     var stack = defined(actualStack, errorStack);
     if (stack) {

test/stackTrace.js

@@ -81,11 +81,11 @@ tap.test('preserves stack trace for failed assertions', function (tt) {
         tt.equal(typeof data.diag.stack, 'string');
         at = data.diag.at || '';
         stack = data.diag.stack || '';
-        tt.ok(/^Error: false should be true(\n    at .+)+/.exec(stack), 'stack should be a stack')
+        tt.ok(/^Error: true should be false(\n    at .+)+/.exec(stack), 'stack should be a stack')
         tt.deepEqual(data, {
             ok: false,
             id: 1,
-            name: "false should be true",
+            name: "true should be false",
             diag: {
                 at: at,
                 stack: stack,
@@ -103,7 +103,7 @@ tap.test('preserves stack trace for failed assertions', function (tt) {
             body,
             'TAP version 13\n'
             + '# t.equal stack trace\n'
-            + 'not ok 1 false should be true\n'
+            + 'not ok 1 true should be false\n'
             + '  ---\n'
             + '    operator: equal\n'
             + '    expected: false\n'
@@ -129,7 +129,72 @@ tap.test('preserves stack trace for failed assertions', function (tt) {
 
     test('t.equal stack trace', function (t) {
         t.plan(1);
-        t.equal(true, false, 'false should be true');
+        t.equal(true, false, 'true should be false');
+    });
+});
+
+tap.test('preserves stack trace for failed assertions where actual===falsy', function (tt) {
+    tt.plan(6);
+
+    var test = tape.createHarness();
+    var stream = test.createStream();
+    var parser = stream.pipe(tapParser());
+
+    var stack = ''
+    parser.once('assert', function (data) {
+        tt.equal(typeof data.diag.at, 'string');
+        tt.equal(typeof data.diag.stack, 'string');
+        at = data.diag.at || '';
+        stack = data.diag.stack || '';
+        tt.ok(/^Error: false should be true(\n    at .+)+/.exec(stack), 'stack should be a stack')
+        tt.deepEqual(data, {
+            ok: false,
+            id: 1,
+            name: "false should be true",
+            diag: {
+                at: at,
+                stack: stack,
+                operator: 'equal',
+                expected: true,
+                actual: false
+            }
+        });
+    });
+
+    stream.pipe(concat(function (body) {
+        var body = body.toString('utf8');
+        body = stripAt(body);
+        tt.equal(
+            body,
+            'TAP version 13\n'
+            + '# t.equal stack trace\n'
+            + 'not ok 1 false should be true\n'
+            + '  ---\n'
+            + '    operator: equal\n'
+            + '    expected: true\n'
+            + '    actual:   false\n'
+            + '    stack: |-\n'
+            + '      '
+            + stack.replace(/\n/g, '\n      ') + '\n'
+            + '  ...\n'
+            + '\n'
+            + '1..1\n'
+            + '# tests 1\n'
+            + '# pass  0\n'
+            + '# fail  1\n'
+        );
+
+        tt.deepEqual(getDiag(body), {
+            stack: stack,
+            operator: 'equal',
+            expected: true,
+            actual: false
+        });
+    }));
+
+    test('t.equal stack trace', function (t) {
+        t.plan(1);
+        t.equal(false, true, 'false should be true');
     });
 });