diff --git a/include/kunit/string-stream.h b/include/kunit/string-stream.h
new file mode 100644
index 0000000000000..0552a05781afe
--- /dev/null
+++ b/include/kunit/string-stream.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * C++ stream style string builder used in KUnit for building messages.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_STRING_STREAM_H
+#define _KUNIT_STRING_STREAM_H
+
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/kref.h>
+#include <stdarg.h>
+
+struct string_stream_fragment {
+	struct list_head node;
+	char *fragment;
+};
+
+struct string_stream {
+	size_t length;
+	struct list_head fragments;
+	/* length and fragments are protected by this lock */
+	spinlock_t lock;
+};
+
+struct kunit;
+
+struct string_stream *alloc_string_stream(struct kunit *test);
+
+void string_stream_get(struct string_stream *stream);
+
+int string_stream_put(struct string_stream *stream);
+
+int string_stream_add(struct string_stream *stream, const char *fmt, ...);
+
+int string_stream_vadd(struct string_stream *stream,
+		       const char *fmt,
+		       va_list args);
+
+char *string_stream_get_string(struct string_stream *stream);
+
+void string_stream_clear(struct string_stream *stream);
+
+bool string_stream_is_empty(struct string_stream *stream);
+
+#endif /* _KUNIT_STRING_STREAM_H */
diff --git a/kunit/Makefile b/kunit/Makefile
index 5efdc4dea2c08..275b565a0e81f 100644
--- a/kunit/Makefile
+++ b/kunit/Makefile
@@ -1 +1,2 @@
-obj-$(CONFIG_KUNIT) +=			test.o
+obj-$(CONFIG_KUNIT) +=			test.o \
+					string-stream.o
diff --git a/kunit/string-stream.c b/kunit/string-stream.c
new file mode 100644
index 0000000000000..0463a92dad74b
--- /dev/null
+++ b/kunit/string-stream.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * C++ stream style string builder used in KUnit for building messages.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <kunit/string-stream.h>
+#include <kunit/test.h>
+
+int string_stream_vadd(struct string_stream *stream,
+		       const char *fmt,
+		       va_list args)
+{
+	struct string_stream_fragment *frag_container;
+	int len;
+	va_list args_for_counting;
+	unsigned long flags;
+
+	/* Make a copy because `vsnprintf` could change it */
+	va_copy(args_for_counting, args);
+
+	/* Need space for null byte. */
+	len = vsnprintf(NULL, 0, fmt, args_for_counting) + 1;
+
+	va_end(args_for_counting);
+
+	frag_container = kmalloc(sizeof(*frag_container), GFP_KERNEL);
+	if (!frag_container)
+		return -ENOMEM;
+
+	frag_container->fragment = kmalloc(len, GFP_KERNEL);
+	if (!frag_container->fragment) {
+		kfree(frag_container);
+		return -ENOMEM;
+	}
+
+	len = vsnprintf(frag_container->fragment, len, fmt, args);
+	spin_lock_irqsave(&stream->lock, flags);
+	stream->length += len;
+	list_add_tail(&frag_container->node, &stream->fragments);
+	spin_unlock_irqrestore(&stream->lock, flags);
+
+	return 0;
+}
+
+int string_stream_add(struct string_stream *stream, const char *fmt, ...)
+{
+	va_list args;
+	int result;
+
+	va_start(args, fmt);
+	result = string_stream_vadd(stream, fmt, args);
+	va_end(args);
+
+	return result;
+}
+
+void string_stream_clear(struct string_stream *stream)
+{
+	struct string_stream_fragment *frag_container, *frag_container_safe;
+	unsigned long flags;
+
+	spin_lock_irqsave(&stream->lock, flags);
+	list_for_each_entry_safe(frag_container,
+				 frag_container_safe,
+				 &stream->fragments,
+				 node) {
+		list_del(&frag_container->node);
+		kfree(frag_container->fragment);
+		kfree(frag_container);
+	}
+	stream->length = 0;
+	spin_unlock_irqrestore(&stream->lock, flags);
+}
+
+char *string_stream_get_string(struct string_stream *stream)
+{
+	struct string_stream_fragment *frag_container;
+	size_t buf_len = stream->length + 1; /* +1 for null byte. */
+	char *buf;
+	unsigned long flags;
+
+	buf = kzalloc(buf_len, GFP_KERNEL);
+	if (!buf)
+		return NULL;
+
+	spin_lock_irqsave(&stream->lock, flags);
+	list_for_each_entry(frag_container, &stream->fragments, node)
+		strlcat(buf, frag_container->fragment, buf_len);
+	spin_unlock_irqrestore(&stream->lock, flags);
+
+	return buf;
+}
+
+bool string_stream_is_empty(struct string_stream *stream)
+{
+	bool is_empty;
+	unsigned long flags;
+
+	spin_lock_irqsave(&stream->lock, flags);
+	is_empty = list_empty(&stream->fragments);
+	spin_unlock_irqrestore(&stream->lock, flags);
+
+	return is_empty;
+}
+
+static int string_stream_init(struct kunit_resource *res, void *context)
+{
+	struct string_stream *stream;
+
+	stream = kzalloc(sizeof(*stream), GFP_KERNEL);
+	if (!stream)
+		return -ENOMEM;
+
+	res->allocation = stream;
+	INIT_LIST_HEAD(&stream->fragments);
+	spin_lock_init(&stream->lock);
+
+	return 0;
+}
+
+static void string_stream_free(struct kunit_resource *res)
+{
+	struct string_stream *stream = res->allocation;
+
+	string_stream_clear(stream);
+	kfree(stream);
+}
+
+struct string_stream *alloc_string_stream(struct kunit *test)
+{
+	struct kunit_resource *res;
+
+	res = kunit_alloc_resource(test,
+				   string_stream_init,
+				   string_stream_free,
+				   NULL);
+
+	if (!res)
+		return NULL;
+
+	return res->allocation;
+}
