diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..a2eb55d
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,5 @@
+root = true
+
+[*.{c,h}]
+indent_style = space
+indent_size = 2
diff --git a/Makefile b/Makefile
index 665c411..9db32d4 100644
--- a/Makefile
+++ b/Makefile
@@ -12,6 +12,7 @@ LIB := $(BUILD_DIR)/$(LIB_FILENAME)
 
 SRCS != find '$(SRC_DIR)' -iname '*.c'
 SRCS_H != find $(INC_DIRS) -iname '*.h'
+SRCS_H_INTERNAL != find $(SRC_DIR) -iname '*.h'
 SRCS_TEST != find '$(TEST_DIR)' -iname '*.c'
 
 OBJS := $(SRCS:%=$(BUILD_DIR)/%.o)
@@ -66,15 +67,9 @@ $(TARGETS_TEST): test-%: %
 $(TARGETS_MEM_TEST): test-mem-%: %
 	valgrind --tool=memcheck --error-exitcode=1 --track-origins=yes --leak-check=full ./$^
 
-test-mem: build-test
-	@ $(foreach bin,$(BINS_TEST),valgrind --tool=memcheck --error-exitcode=1 \
-		--track-origins=yes --leak-check=full ./$(bin);)
-
 .PHONY: build-test
 build-test: $(BINS_TEST)
 
-# For simplicity, we link every object file to each of the test files. This
-# might be changed later if this starts to become too slow.
 $(BINS_TEST): %: %.c.o $(LIB)
 	$(CC) \
 		$^ -o $@
@@ -92,11 +87,11 @@ $(BUILD_DIR)/$(TEST_DIR)/%.c.o: $(TEST_DIR)/%.c
 # =====MAINTENANCE=====
 .PHONY: lint
 lint:
-	clang-format -n --Werror $(SRCS) $(SRCS_H)
+	clang-format -n --Werror $(SRCS) $(SRCS_H) $(SRCS_H_INTERNAL)
 
 .PHONY: fmt
 fmt:
-	clang-format -i $(SRCS) $(SRCS_H)
+	clang-format -i $(SRCS) $(SRCS_H) $(SRCS_H_INTERNAL)
 
 .PHONY: clean
 clean:
diff --git a/include/vieter_job_queue.h b/include/vieter_job_queue.h
new file mode 100644
index 0000000..6cd748f
--- /dev/null
+++ b/include/vieter_job_queue.h
@@ -0,0 +1,127 @@
+#ifndef VIETER_JOB_QUEUE
+#define VIETER_JOB_QUEUE
+
+#include "vieter_cron.h"
+#include <stdbool.h>
+#include <stdint.h>
+
+/*
+ * The order of these do not imply that they happen in this order. New states
+ * will just get added as consecutive numbers. Their values should be
+ * monotonically increasing values, as these will be used to index arrays, among
+ * other things.
+ */
+typedef enum vieter_job_state {
+  vieter_job_state_queued = 0,
+  vieter_job_state_ready = 1,
+  vieter_job_state_build_finished = 2,
+  vieter_job_state_failed = 3
+} vieter_job_state;
+
+// This macro should be kept in sync with the above enum
+#define VIETER_JOB_STATES 4
+#define VIETER_JOB_INITIAL_STATE vieter_job_state_queued
+#define VIETER_JOB_FAILURE_STATE vieter_job_state_failed
+
+/*
+ * Struct storing a report for why a certain job failed to be processed in the
+ * given state.
+ */
+typedef struct vieter_job_failure_report {
+  vieter_job_state failed_state;
+  char *msg;
+} vieter_job_failure_report;
+
+vieter_job_failure_report *vieter_job_failure_report_init();
+
+void vieter_job_failure_report_free(vieter_job_failure_report **ptp);
+
+/*
+ * Represents a job currently being processed in the system. A job migrates
+ * between different states before finally being removed from the queue.
+ */
+typedef struct vieter_job {
+  uint64_t id;
+  uint64_t next_scheduled_time;
+  vieter_cron_expression *schedule;
+  void *build_config;
+  vieter_job_failure_report *failure_report;
+  uint64_t state_transition_times[VIETER_JOB_STATES];
+  vieter_job_state current_state;
+  bool single;
+  bool dispatched;
+} vieter_job;
+
+/*
+ * Allocate a new vieter_job object.
+ */
+vieter_job *vieter_job_init();
+
+void vieter_job_free(vieter_job **ptp);
+
+/*
+ * Represents the actual queue managing the list of jobs.
+ */
+typedef struct vieter_job_queue vieter_job_queue;
+
+typedef enum vieter_job_queue_error {
+  vieter_job_queue_ok = 0,
+  vieter_job_queue_not_present = 1,
+  vieter_job_queue_already_present = 2,
+  vieter_job_queue_state_empty = 3,
+  vieter_job_queue_not_dispatched = 4
+} vieter_job_queue_error;
+
+/*
+ * Allocate and initialize a new job queue.
+ */
+vieter_job_queue *vieter_job_queue_init();
+
+/*
+ * Free a job queue.
+ */
+void vieter_job_queue_free(vieter_job_queue **ptp);
+
+/*
+ * Insert the given job into the system.
+ */
+vieter_job_queue_error vieter_job_queue_insert(vieter_job_queue *queue,
+                                               vieter_job *job);
+
+/*
+ * Pop a job from the given state's queue. The job will then be marked as
+ * dispatched.
+ */
+vieter_job_queue_error vieter_job_queue_pop(vieter_job **out,
+                                            vieter_job_queue *queue,
+                                            vieter_job_state state);
+
+/*
+ * Transition the job with the given id to the new state. This sets the
+ * job's dispatch flag to false, and adds it to the new state's queue.
+ *
+ * NOTE: this can only be done with dispatched jobs.
+ */
+vieter_job_queue_error vieter_job_queue_transition(vieter_job_queue *queue,
+                                                   uint64_t id,
+                                                   vieter_job_state new_state);
+
+/*
+ * Remove the given job from the job queue, returning its pointer to the caller.
+ *
+ * NOTE: this can only be done with dispatched jobs.
+ */
+vieter_job_queue_error
+vieter_job_queue_remove(vieter_job **out, vieter_job_queue *queue, uint64_t id);
+
+/*
+ * Transition a job into the failure state, and attach a failure report with the
+ * provided message. The message is copied, so the caller is responsible for
+ * freeing the provided string.
+ *
+ * NOTE: this can only be done with dispatched jobs.
+ */
+vieter_job_queue_error vieter_job_queue_fail(vieter_job_queue *queue,
+                                             uint64_t id, char *report_message);
+
+#endif
diff --git a/include/vieter_tree.h b/include/vieter_tree.h
index d3abd2f..4da500f 100644
--- a/include/vieter_tree.h
+++ b/include/vieter_tree.h
@@ -9,7 +9,8 @@ typedef struct vieter_tree vieter_tree;
 typedef enum vieter_tree_error {
   vieter_tree_ok = 0,
   vieter_tree_already_present = 1,
-  vieter_tree_not_present = 2
+  vieter_tree_not_present = 2,
+  vieter_tree_iterator_done = 3
 } vieter_tree_error;
 
 /*
@@ -45,4 +46,43 @@ vieter_tree_error vieter_tree_remove(void **out, vieter_tree *tree,
  */
 uint64_t vieter_tree_size(vieter_tree *tree);
 
+/*
+ * An iterator that can be used to traverse a tree in-order.
+ */
+typedef struct vieter_tree_iterator vieter_tree_iterator;
+
+/*
+ * Allocate and initialize a new iterator from the given tree.
+ */
+vieter_tree_iterator *vieter_tree_iterator_from(vieter_tree *tree);
+
+/*
+ * Free an iterator.
+ */
+void vieter_tree_iterator_free(vieter_tree_iterator **ptp);
+
+/*
+ * Return the iterator's next element.
+ */
+vieter_tree_error vieter_tree_iterator_next(void **out,
+                                            vieter_tree_iterator *iter);
+
+/*
+ * Acquire a read lock on the tree. Return value is the result of
+ * pthread_rwlock_rdlock.
+ */
+int vieter_tree_rlock(vieter_tree *tree);
+
+/*
+ * Acquire a write lock on the tree. Return value is the result of
+ * pthread_rwlock_wrlock.
+ */
+int vieter_tree_wlock(vieter_tree *tree);
+
+/*
+ * Unlock the lock after having acquired it. Return value is the result of
+ * pthread_rwlock_unlock.
+ */
+int vieter_tree_unlock(vieter_tree *tree);
+
 #endif
diff --git a/src/heap/vieter_heap_tree.h b/src/heap/vieter_heap_tree.h
index 0a299db..615491a 100644
--- a/src/heap/vieter_heap_tree.h
+++ b/src/heap/vieter_heap_tree.h
@@ -5,16 +5,16 @@
 #include <stdlib.h>
 
 typedef struct vieter_heap_node {
-    uint64_t key;
-    void *data;
-    struct vieter_heap_node *largest_order;
-    union {
-      // Roots point to next tree in the heap, other nodes point to their first
-      // neighbour.
-      struct vieter_heap_node *next_tree;
-      struct vieter_heap_node *next_largest_order;
-    } ptr;
-    uint8_t order;
+  uint64_t key;
+  void *data;
+  struct vieter_heap_node *largest_order;
+  union {
+    // Roots point to next tree in the heap, other nodes point to their first
+    // neighbour.
+    struct vieter_heap_node *next_tree;
+    struct vieter_heap_node *next_largest_order;
+  } ptr;
+  uint8_t order;
 } vieter_heap_node;
 
 /*
@@ -36,7 +36,8 @@ void vieter_heap_tree_free(vieter_heap_node *root);
  * Given the roots of the smallest trees in two heaps, merge them into a single
  * large heap.
  */
-vieter_heap_node *vieter_heap_tree_merge(vieter_heap_node *root_a, vieter_heap_node *root_b);
+vieter_heap_node *vieter_heap_tree_merge(vieter_heap_node *root_a,
+                                         vieter_heap_node *root_b);
 
 /*
  * Given the roots of two trees of the same order, merge them into a heap of one
diff --git a/src/job-queue/README.md b/src/job-queue/README.md
new file mode 100644
index 0000000..8fa9c94
--- /dev/null
+++ b/src/job-queue/README.md
@@ -0,0 +1,27 @@
+The goal of this job queue design is to process jobs in order, with each job
+moving through a pipeline of tasks that need to be completed.
+
+At any given time, a job is in one of a few given states, e.g. "queued". These
+states are explained below. Along with this, each job also has a "dispatched"
+flag. If this flag is set to true, it means this job is currently being
+processed. "Being processed" could mean anything; it depends entirely on the
+state a job's in. While a job is dispatched, it is no longer present in the
+priority queue of its respective state.
+
+## Job
+
+A job describes a scheduled build as it moves through the pipeline of states.
+The job queue datastructure keeps track of all jobs in a central red-black
+binary tree. For each state, a priority queue tracks in what order jobs should
+be processed.
+
+## States
+
+* `queued`: a job that's in the job queue but does not yet need to be executed
+  (as defined by its timestamp)
+* `ready`: a job that's scheduled for building, with all preprocessing tasks
+  fulfilled.
+* `build_finished`: a job whose build has finished, and is waiting for any
+  post-build tasks.
+* `failed`: a job whose processing failed at some point. Jobs in this state
+  include a failure report that describes in what state they failed, and why.
diff --git a/src/job-queue/vieter_job_queue.c b/src/job-queue/vieter_job_queue.c
new file mode 100644
index 0000000..14ae1dc
--- /dev/null
+++ b/src/job-queue/vieter_job_queue.c
@@ -0,0 +1,153 @@
+#include "vieter_job_queue_internal.h"
+
+vieter_job_queue *vieter_job_queue_init() {
+  vieter_job_queue *queue = malloc(sizeof(vieter_job_queue));
+
+  queue->tree = vieter_tree_init();
+
+  for (int i = 0; i < VIETER_JOB_STATES; i++) {
+    queue->heaps[i] = vieter_heap_init();
+  }
+
+  return queue;
+}
+
+void vieter_job_queue_free(vieter_job_queue **ptp) {
+  vieter_job_queue *queue = *ptp;
+
+  vieter_tree_free(queue->tree);
+
+  for (int i = 0; i < VIETER_JOB_STATES; i++) {
+    vieter_heap_free(queue->heaps[i]);
+  }
+
+  free(queue);
+  *ptp = NULL;
+}
+
+vieter_job *vieter_job_init() { return calloc(1, sizeof(vieter_job)); }
+
+void vieter_job_free(vieter_job **ptp) {
+  vieter_job *job = *ptp;
+
+  if (job->schedule != NULL) {
+    vieter_cron_expr_free(job->schedule);
+  }
+
+  if (job->failure_report != NULL) {
+    vieter_job_failure_report_free(&job->failure_report);
+  }
+
+  free(job);
+
+  *ptp = NULL;
+}
+
+vieter_job_queue_error vieter_job_queue_insert(vieter_job_queue *queue,
+                                               vieter_job *job) {
+  vieter_tree_error tree_res = vieter_tree_insert(queue->tree, job->id, job);
+
+  if (tree_res != vieter_tree_ok) {
+    return vieter_job_queue_already_present;
+  }
+
+  vieter_heap_insert(queue->heaps[VIETER_JOB_INITIAL_STATE], job->id, job);
+
+  job->current_state = VIETER_JOB_INITIAL_STATE;
+  job->dispatched = false;
+  job->state_transition_times[VIETER_JOB_INITIAL_STATE] = time(NULL);
+
+  return vieter_job_queue_ok;
+}
+
+vieter_job_queue_error vieter_job_queue_pop(vieter_job **out,
+                                            vieter_job_queue *queue,
+                                            vieter_job_state state) {
+  vieter_heap_error res = vieter_heap_pop((void **)out, queue->heaps[state]);
+
+  if (res != vieter_heap_ok) {
+    return vieter_job_queue_state_empty;
+  }
+
+  (*out)->dispatched = true;
+
+  return vieter_job_queue_ok;
+}
+
+vieter_job_queue_error vieter_job_queue_transition(vieter_job_queue *queue,
+                                                   uint64_t id,
+                                                   vieter_job_state new_state) {
+  vieter_job *job;
+
+  vieter_tree_error res = vieter_tree_search((void **)&job, queue->tree, id);
+
+  if (res != vieter_tree_ok) {
+    return vieter_job_queue_not_present;
+  }
+
+  if (!job->dispatched) {
+    return vieter_job_queue_not_dispatched;
+  }
+
+  vieter_heap_insert(queue->heaps[new_state], job->id, job);
+
+  job->current_state = new_state;
+  job->dispatched = false;
+  job->state_transition_times[new_state] = time(NULL);
+
+  return vieter_job_queue_ok;
+}
+
+vieter_job_queue_error vieter_job_queue_remove(vieter_job **out,
+                                               vieter_job_queue *queue,
+                                               uint64_t id) {
+  vieter_tree_error res = vieter_tree_search((void **)out, queue->tree, id);
+
+  if (res != vieter_tree_ok) {
+    return vieter_job_queue_not_present;
+  }
+
+  vieter_job *job = *out;
+
+  if (!job->dispatched) {
+    return vieter_job_queue_not_dispatched;
+  }
+
+  // This can't fail if the search succeeded
+  vieter_tree_remove((void **)out, queue->tree, job->id);
+
+  return vieter_job_queue_ok;
+}
+
+vieter_job_failure_report *vieter_job_failure_report_init() {
+  return calloc(1, sizeof(vieter_job_failure_report));
+}
+
+vieter_job_queue_error vieter_job_queue_fail(vieter_job_queue *queue,
+                                             uint64_t id,
+                                             char *report_message) {
+  vieter_job *job;
+
+  vieter_tree_error res = vieter_tree_search((void **)&job, queue->tree, id);
+
+  if (res != vieter_tree_ok) {
+    return vieter_job_queue_not_present;
+  }
+
+  if (!job->dispatched) {
+    return vieter_job_queue_not_dispatched;
+  }
+
+  vieter_heap_insert(queue->heaps[VIETER_JOB_FAILURE_STATE], job->id, job);
+
+  job->dispatched = false;
+  job->state_transition_times[VIETER_JOB_FAILURE_STATE] = time(NULL);
+
+  job->failure_report = vieter_job_failure_report_init();
+  job->failure_report->failed_state = job->current_state;
+  job->failure_report->msg = strdup(report_message);
+
+  job->current_state = VIETER_JOB_FAILURE_STATE;
+
+  return vieter_job_queue_ok;
+}
diff --git a/src/job-queue/vieter_job_queue_internal.h b/src/job-queue/vieter_job_queue_internal.h
new file mode 100644
index 0000000..dac8b97
--- /dev/null
+++ b/src/job-queue/vieter_job_queue_internal.h
@@ -0,0 +1,13 @@
+#ifndef VIETER_JOB_QUEUE_INTERNAL
+#define VIETER_JOB_QUEUE_INTERNAL
+
+#include "vieter_heap.h"
+#include "vieter_job_queue.h"
+#include "vieter_tree.h"
+
+struct vieter_job_queue {
+  vieter_tree *tree;
+  vieter_heap *heaps[VIETER_JOB_STATES];
+};
+
+#endif
diff --git a/src/tree/vieter_tree.c b/src/tree/vieter_tree.c
index eef2aef..ca6016e 100644
--- a/src/tree/vieter_tree.c
+++ b/src/tree/vieter_tree.c
@@ -1,11 +1,5 @@
-#include "vieter_tree_internal.h"
-#include "vieter_tree_node.h"
 #include "vieter_tree_balancing.h"
-
-struct vieter_tree {
-  uint64_t size;
-  vieter_tree_node *root;
-};
+#include "vieter_tree_internal.h"
 
 vieter_tree *vieter_tree_init() { return calloc(1, sizeof(vieter_tree)); }
 
@@ -120,3 +114,15 @@ bool vieter_tree_validate(vieter_tree *tree) {
   return vieter_tree_node_get(tree->root, vieter_tree_node_black) &&
          vieter_tree_node_validate(tree->root, 0, expected_black_nodes);
 }
+
+int vieter_tree_rlock(vieter_tree *tree) {
+  return pthread_rwlock_rdlock(&tree->lock);
+}
+
+int vieter_tree_wlock(vieter_tree *tree) {
+  return pthread_rwlock_wrlock(&tree->lock);
+}
+
+int vieter_tree_unlock(vieter_tree *tree) {
+  return pthread_rwlock_unlock(&tree->lock);
+}
diff --git a/src/tree/vieter_tree_internal.h b/src/tree/vieter_tree_internal.h
index 670d45b..037345c 100644
--- a/src/tree/vieter_tree_internal.h
+++ b/src/tree/vieter_tree_internal.h
@@ -1,10 +1,24 @@
 #include "vieter_tree.h"
+#include "vieter_tree_node.h"
 
+#include <pthread.h>
 #include <stdbool.h>
 
+struct vieter_tree {
+  uint64_t size;
+  vieter_tree_node *root;
+  pthread_rwlock_t lock;
+};
+
 /*
  * Inspect whether the tree is still a valid red-black-tree.
  *
  * @return true if valid, false otherwise.
  */
 bool vieter_tree_validate(vieter_tree *tree);
+
+struct vieter_tree_iterator {
+  vieter_tree_node *current_node;
+  bool started;
+  bool done;
+};
diff --git a/src/tree/vieter_tree_iterator.c b/src/tree/vieter_tree_iterator.c
new file mode 100644
index 0000000..4eefe02
--- /dev/null
+++ b/src/tree/vieter_tree_iterator.c
@@ -0,0 +1,49 @@
+#include "vieter_tree.h"
+#include "vieter_tree_internal.h"
+
+vieter_tree_iterator *vieter_tree_iterator_from(vieter_tree *tree) {
+  vieter_tree_iterator *iter = calloc(1, sizeof(vieter_tree_iterator));
+
+  // An empty tree's iterator will be done immediately
+  if (tree->size == 0) {
+    iter->started = true;
+    iter->done = true;
+
+    return iter;
+  }
+
+  iter->current_node = tree->root;
+
+  return iter;
+}
+
+vieter_tree_error vieter_tree_iterator_next(void **out,
+                                            vieter_tree_iterator *iter) {
+  if (iter->done) {
+    return vieter_tree_iterator_done;
+  }
+
+  if (!iter->started) {
+    while (iter->current_node->children[0] != NULL) {
+      iter->current_node = iter->current_node->children[0];
+    }
+
+    iter->started = true;
+  }
+
+  *out = iter->current_node->data;
+
+  iter->current_node = vieter_tree_node_next(iter->current_node);
+
+  if (iter->current_node == NULL) {
+    iter->done = true;
+  }
+
+  return vieter_tree_ok;
+}
+
+void vieter_tree_iterator_free(vieter_tree_iterator **ptp) {
+  free(*ptp);
+
+  *ptp = NULL;
+}
diff --git a/src/tree/vieter_tree_node.c b/src/tree/vieter_tree_node.c
index e58092e..0a8e658 100644
--- a/src/tree/vieter_tree_node.c
+++ b/src/tree/vieter_tree_node.c
@@ -150,3 +150,22 @@ void vieter_tree_node_set(vieter_tree_node *node, vieter_tree_node_flag flag,
 bool vieter_tree_node_get(vieter_tree_node *node, vieter_tree_node_flag flag) {
   return (node->flags & flag) != 0;
 }
+
+vieter_tree_node *vieter_tree_node_next(vieter_tree_node *node) {
+  if (node->children[1] != NULL) {
+    node = node->children[1];
+
+    while (node->children[0] != NULL) {
+      node = node->children[0];
+    }
+
+    return node;
+  }
+
+  while (node->parent != NULL &&
+         vieter_tree_node_get(node, vieter_tree_node_right)) {
+    node = node->parent;
+  }
+
+  return node->parent;
+}
diff --git a/src/tree/vieter_tree_node.h b/src/tree/vieter_tree_node.h
index 3b1c169..4db3cfe 100644
--- a/src/tree/vieter_tree_node.h
+++ b/src/tree/vieter_tree_node.h
@@ -2,8 +2,8 @@
 #define VIETER_TREE_NODE
 
 #include "vieter_tree.h"
-#include <stdint.h>
 #include <stdbool.h>
+#include <stdint.h>
 
 typedef enum vieter_tree_node_flag {
   vieter_tree_node_black = ((uint8_t)1) << 0,
@@ -13,11 +13,11 @@ typedef enum vieter_tree_node_flag {
 } vieter_tree_node_flag;
 
 typedef struct vieter_tree_node {
-    uint64_t key;
-    void *data;
-    struct vieter_tree_node *parent;
-    struct vieter_tree_node *children[2];
-    uint8_t flags;
+  uint64_t key;
+  void *data;
+  struct vieter_tree_node *parent;
+  struct vieter_tree_node *children[2];
+  uint8_t flags;
 } vieter_tree_node;
 
 /*
@@ -33,27 +33,33 @@ void vieter_tree_node_free(vieter_tree_node *node);
 /*
  * Insert a new key into the given tree.
  */
-vieter_tree_error vieter_tree_node_insert(vieter_tree_node *root, uint64_t key, void *data);
+vieter_tree_error vieter_tree_node_insert(vieter_tree_node *root, uint64_t key,
+                                          void *data);
 
 /*
  * Return the node representing the requested value.
  */
-vieter_tree_error vieter_tree_node_search_node(vieter_tree_node **out, vieter_tree_node *root, uint64_t key);
+vieter_tree_error vieter_tree_node_search_node(vieter_tree_node **out,
+                                               vieter_tree_node *root,
+                                               uint64_t key);
 
 /*
  * Search for the data represented by the given key.
  */
-vieter_tree_error vieter_tree_node_search(void **out, vieter_tree_node *root, uint64_t key);
+vieter_tree_error vieter_tree_node_search(void **out, vieter_tree_node *root,
+                                          uint64_t key);
 
 /*
  * Remove the data associated with the given key.
  */
-vieter_tree_error vieter_tree_node_remove(void **out, vieter_tree_node **root_ptr, uint64_t key);
+vieter_tree_error
+vieter_tree_node_remove(void **out, vieter_tree_node **root_ptr, uint64_t key);
 
 /*
  * Set a node's bit flag to the given value.
  */
-void vieter_tree_node_set(vieter_tree_node *node, vieter_tree_node_flag flag, bool value);
+void vieter_tree_node_set(vieter_tree_node *node, vieter_tree_node_flag flag,
+                          bool value);
 
 /*
  * Get whether a node's bit flag is set.
@@ -70,11 +76,19 @@ void vieter_tree_node_add_child(vieter_tree_node *parent, uint64_t key,
 /*
  * Replace a node's children array.
  */
-void vieter_tree_node_set_children(vieter_tree_node *parent, vieter_tree_node **children);
+void vieter_tree_node_set_children(vieter_tree_node *parent,
+                                   vieter_tree_node **children);
 
 /*
  * Set a node's left or right child to the given node.
  */
-void vieter_tree_node_set_child(vieter_tree_node *parent, vieter_tree_node *child, bool right);
+void vieter_tree_node_set_child(vieter_tree_node *parent,
+                                vieter_tree_node *child, bool right);
+
+/*
+ * Return the in-order successor of the given node, or NULL if it's the last
+ * node in the tree.
+ */
+vieter_tree_node *vieter_tree_node_next(vieter_tree_node *node);
 
 #endif
diff --git a/test/tree/test_tree.c b/test/tree/test_tree.c
index 2ab6870..10235cb 100644
--- a/test/tree/test_tree.c
+++ b/test/tree/test_tree.c
@@ -16,19 +16,30 @@ void test_insert() {
     vieter_tree *tree = vieter_tree_init();
 
     for (uint64_t i = 0; i < 250; i++) {
-        TEST_CHECK(vieter_tree_insert(tree, i, NULL) == vieter_tree_ok);
+        TEST_CHECK(vieter_tree_insert(tree, i, (void *)i) == vieter_tree_ok);
         TEST_SIZE(tree, i + 1);
         TEST_CHECK(vieter_tree_validate(tree));
     }
 
-    void *out;
+    vieter_tree_iterator *iter = vieter_tree_iterator_from(tree);
+
+    void *out = NULL;
 
     for (uint64_t i = 0; i < 250; i++) {
         TEST_CHECK(vieter_tree_search(&out, tree, i) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)i);
         TEST_CHECK(vieter_tree_insert(tree, i, NULL) == vieter_tree_already_present);
         TEST_CHECK(vieter_tree_search(&out, tree, i) == vieter_tree_ok);
+
+        out = NULL;
+
+        TEST_CHECK(vieter_tree_iterator_next(&out, iter) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)i);
     }
 
+    TEST_CHECK(vieter_tree_iterator_next(&out, iter) == vieter_tree_iterator_done);
+
+    vieter_tree_iterator_free(&iter);
     vieter_tree_free(tree);
 }
 
diff --git a/test/tree/test_tree_random.c b/test/tree/test_tree_random.c
new file mode 100644
index 0000000..d1b9ab0
--- /dev/null
+++ b/test/tree/test_tree_random.c
@@ -0,0 +1,59 @@
+#include "acutest.h"
+#include "vieter_tree_internal.h"
+
+#define TEST_SIZE(tree, size) \
+    TEST_CHECK(vieter_tree_size(tree) == size); \
+    TEST_MSG("Size: %zu", vieter_tree_size(tree))
+
+int uint64_t_compare(const void *a, const void *b) {
+    if ((*(uint64_t *)a) < (*(uint64_t *)b)) {
+        return -1;
+    } else if ((*(uint64_t *)a) > (*(uint64_t *)b)) {
+        return 1;
+    } else {
+        return 0;
+    }
+}
+
+void test_insert_random() {
+    const uint64_t n = 1000;
+    srand(0);
+
+    vieter_tree *tree = vieter_tree_init();
+
+    uint64_t *numbers = malloc(n * sizeof(uint64_t));
+    uint64_t num;
+    void *out = NULL;
+
+    for (uint64_t i = 0; i < n; i++) {
+        num = rand();
+        vieter_tree_insert(tree, num, (void *)num);
+        TEST_SIZE(tree, i + 1);
+        TEST_CHECK(vieter_tree_validate(tree));
+        TEST_CHECK(vieter_tree_search(&out, tree, num) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)num);
+
+        out = NULL;
+
+        numbers[i] = num;
+    }
+
+    qsort(numbers, n, sizeof(uint64_t), uint64_t_compare);
+
+    vieter_tree_iterator *iter = vieter_tree_iterator_from(tree);
+    out = NULL;
+
+    for (uint64_t i = 0; i < n; i++) {
+        TEST_CHECK(vieter_tree_iterator_next(&out, iter) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)numbers[i]);
+    }
+
+    free(numbers);
+    vieter_tree_iterator_free(&iter);
+    vieter_tree_free(tree);
+}
+
+TEST_LIST = {
+    {"tree insert random", test_insert_random},
+    {NULL, NULL}
+};