diff --git a/.woodpecker/lint.yml b/.woodpecker/lint.yml
new file mode 100644
index 0000000..b9d2806
--- /dev/null
+++ b/.woodpecker/lint.yml
@@ -0,0 +1,16 @@
+variables:
+  &image 'git.rustybever.be/chewing_bever/c-devop:alpine3.17'
+
+branches:
+  exclude: [ main ]
+platform: linux/amd64
+
+pipeline:
+  lint:
+    image: *image
+    pull: true
+    commands:
+      - make lint
+      - make objs CFLAGS='-Werror -fsyntax-only'
+    when:
+      event: [push, pull_request]
diff --git a/.woodpecker/test-mem.yml b/.woodpecker/test-mem.yml
new file mode 100644
index 0000000..48896a5
--- /dev/null
+++ b/.woodpecker/test-mem.yml
@@ -0,0 +1,20 @@
+variables:
+  &image 'git.rustybever.be/chewing_bever/c-devop:alpine3.17'
+
+branches:
+  exclude: [ main ]
+platform: linux/amd64
+
+depends_on:
+  - test
+
+pipeline:
+  test:
+    image: *image
+    pull: true
+    commands:
+      - make test-mem
+      - make clean
+      - make test-mem CFLAGS='-O3 -Werror -Wall'
+    when:
+      event: [push, pull_request]
diff --git a/.woodpecker.yml b/.woodpecker/test.yml
similarity index 58%
rename from .woodpecker.yml
rename to .woodpecker/test.yml
index a7e8fe3..a603923 100644
--- a/.woodpecker.yml
+++ b/.woodpecker/test.yml
@@ -11,26 +11,12 @@ branches:
 platform: ${PLATFORM}
 
 pipeline:
-  lint:
+  build-and-test:
     image: *image
     pull: true
-    commands:
-      - make lint
-    when:
-      event: [push, pull_request]
-
-  build:
-    image: *image
-    commands:
-      - make
-      - make clean
-      - CFLAGS='-O3' make
-    when:
-      event: [push, pull_request]
-
-  test:
-    image: *image
     commands:
       - make test
+      - make clean
+      - make test CFLAGS='-O3 -Werror -Wall'
     when:
       event: [push, pull_request]
diff --git a/Makefile b/Makefile
index 4907163..04c6dd3 100644
--- a/Makefile
+++ b/Makefile
@@ -8,6 +8,8 @@ SRC_DIR ?= src
 TEST_DIR ?= test
 INC_DIRS ?= include
 
+LIB := $(BUILD_DIR)/$(LIB_FILENAME)
+
 SRCS != find '$(SRC_DIR)' -iname '*.c'
 SRCS_H != find $(INC_DIRS) -iname '*.h'
 SRCS_TEST != find '$(TEST_DIR)' -iname '*.c'
@@ -17,6 +19,8 @@ OBJS_TEST := $(SRCS_TEST:%=$(BUILD_DIR)/%.o)
 DEPS := $(SRCS:%=$(BUILD_DIR)/%.d) $(SRCS_TEST:%=$(BUILD_DIR)/%.d)
 
 BINS_TEST := $(OBJS_TEST:%.c.o=%)
+TARGETS_TEST := $(BINS_TEST:%=test-%)
+TARGETS_MEM_TEST := $(BINS_TEST:%=test-mem-%)
 
 INC_FLAGS := $(addprefix -I,$(INC_DIRS))
 
@@ -25,42 +29,61 @@ INC_FLAGS := $(addprefix -I,$(INC_DIRS))
 #  object file is also recompiled if only a header is changed.
 # -MP: generate a dummy target for every header file (according to the  docs it
 #  prevents some errors when removing header files)
-CFLAGS ?= -MMD -MP -Wall -Werror -Wextra
-CFLAGS += $(INC_FLAGS)
+CFLAGS ?= -MMD -MP -g
+VIETERCFLAGS := $(INC_FLAGS) $(CFLAGS) -Wall -Wextra
 
 .PHONY: all
 all: vieter
 
 
 # =====COMPILATION=====
+# Utility used by the CI to lint
+.PHONY: objs
+objs: $(OBJS)
+
 .PHONY: vieter
-vieter: $(BUILD_DIR)/$(LIB_FILENAME)
+vieter: $(LIB)
 $(BUILD_DIR)/$(LIB_FILENAME): $(OBJS)
 	ar -rcs $@ $(OBJS)
 
 $(BUILD_DIR)/$(SRC_DIR)/%.c.o: $(SRC_DIR)/%.c
 	mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(VIETERCFLAGS) -c $< -o $@
 
 
 # =====TESTING=====
 .PHONY: test
-test: build-test
-	@ $(foreach bin,$(BINS_TEST),./$(bin);)
+test: $(TARGETS_TEST)
+
+.PHONY: test-mem
+test-mem: $(TARGETS_MEM_TEST)
+
+.PHONY: $(TARGETS_TEST)
+$(TARGETS_TEST): test-%: %
+	./$^
+
+.PHONY: $(TARGETS_MEM_TEST)
+$(TARGETS_MEM_TEST): test-mem-%: %
+	valgrind --tool=memcheck --error-exitcode=1 --track-origins=yes --leak-check=full ./$^
 
 .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 $(OBJS)
-	$(CC) $^ -o $@
+$(BINS_TEST): %: %.c.o $(LIB)
+	$(CC) \
+		$^ -o $@
 
-# Each test includes the test directory, which contains the acutest header file
+# Along with the include directory, each test includes $(TEST_DIR) (which
+# contains the acutest.h header file), and the src directory of the module it's
+# testing. This allows tests to access internal methods, which aren't publicly
+# exposed.
 $(BUILD_DIR)/$(TEST_DIR)/%.c.o: $(TEST_DIR)/%.c
 	mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -I$(TEST_DIR) -c $< -o $@
-
+	$(CC) $(VIETERCFLAGS) -I$(TEST_DIR) \
+		-I$(dir $(@:$(BUILD_DIR)/$(TEST_DIR)/%=$(SRC_DIR)/%)) \
+		-c $< -o $@
 
 # =====MAINTENANCE=====
 .PHONY: lint
diff --git a/README.md b/README.md
index 724ba54..d1fef1a 100644
--- a/README.md
+++ b/README.md
@@ -1,15 +1,12 @@
 # libvieter
 
-This library powers part of Vieter, most noteably the sections that can easily
+This library powers part of Vieter, most notably the sections that can easily
 be implemented in C (or just parts I want to implement in C because it's fun).
 
-The goal of this library is to be completely self-contained, meaning any
-required data structures have to be implemented as well. It can only depend on
-the C standard libraries.
+The goal of this library is to be as self-contained as possible; data
+structures should be implemented manually if possible.
 
-Currently it contains the following:
-
-* Cron expression parser & next time calculator
+See the [source code](src) for the list of modules.
 
 ## Development
 
@@ -18,13 +15,41 @@ Currently it contains the following:
 Everything is handled by the provided Makefile. To compile the static library,
 simply run `make`.
 
+### Project structure
+
+Each module has its own subdirectory inside `src`, e.g. `src/cron`. This
+directory contains the actual implementation of a module, along with any
+internally used header files. Each internal function should be defined in a
+header file, as to make testing these possible.
+
+Each module should also have its own header file inside the `include`
+directory. This header file defines the public API that the library exposes for
+this specific module.
+
+Any code in a module may only import internal headers from that module, along
+with any of the public API header files. Modules should not depend on each
+other's internal implementationns.
+
+Each module should contain a README describing its contents.
+
+All file names, function names... (even internals) should follow snake case
+convention and have a prefix unique to that module, starting with `vieter_`.
+For example, the `cron` modules uses the `vieter_cron_` prefix for everything.
+
+Header files should only import what they explicitely need. If some function is
+only used in a .c file, the import should be placed in the .c file instead.
+
 ### Testing
 
 This library uses [Acutest](https://github.com/mity/acutest) for its tests.
 Tests should be placed in the `test` subdirectory, further divided into
-directories that correspond those in `src`. Test files should begin with
+directories that correspond to those in `src`. Test files should begin with
 `test_`, and their format should follow the expected format for Acutest.
 
+Each `test_` is compiled separately into a binary, linked with libvieter. A
+test file can import any of the public API header files, along with any header
+files defined in its respective module. This allows testing internal functions.
+
 To run the tests, simply run `make test`. If you wish to only run a specific
 test binary, you can find them in `build/test`.
 
diff --git a/include/vieter_cron.h b/include/vieter_cron.h
index 9088d4d..459a49f 100644
--- a/include/vieter_cron.h
+++ b/include/vieter_cron.h
@@ -1,7 +1,6 @@
 #ifndef VIETER_CRON
 #define VIETER_CRON
 
-#include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
@@ -35,18 +34,38 @@ typedef struct vieter_cron_simple_time {
   int minute;
 } vieter_cron_simple_time;
 
-vieter_cron_expression *ce_init();
+/*
+ * Allocate and initialize a new empty cron expression.
+ */
+vieter_cron_expression *vieter_cron_expr_init();
 
+/*
+ * Deallocate a cron expression.
+ */
 void vieter_cron_expr_free(vieter_cron_expression *ce);
 
+/*
+ * Given a cron expression and a reference time, calculate the next time after
+ * the reference time that this expression matches.
+ */
 void vieter_cron_expr_next(vieter_cron_simple_time *out,
                            vieter_cron_expression *ce,
                            vieter_cron_simple_time *ref);
 
+/*
+ * Convencience wrapper around vieter_cron_expr_next that uses the current time
+ * as the reference time.
+ */
 void vieter_cron_expr_next_from_now(vieter_cron_simple_time *out,
                                     vieter_cron_expression *ce);
 
-enum vieter_cron_parse_error vieter_cron_expr_parse(vieter_cron_expression *out,
-                                                    const char *expression);
+/*
+ * Try to parse a string into a cron expression. Note that the cron expression
+ * is updated in-place, meaning it can contain invalid information if the
+ * function returns an error. The cron expression should only be used if the
+ * function succeeded.
+ */
+vieter_cron_parse_error vieter_cron_expr_parse(vieter_cron_expression *out,
+                                               const char *expression);
 
 #endif
diff --git a/include/vieter_heap.h b/include/vieter_heap.h
new file mode 100644
index 0000000..ce6f3a4
--- /dev/null
+++ b/include/vieter_heap.h
@@ -0,0 +1,62 @@
+#ifndef VIETER_HEAP
+#define VIETER_HEAP
+
+#include <stdint.h>
+
+typedef struct vieter_heap vieter_heap;
+
+typedef enum vieter_heap_error {
+  vieter_heap_ok = 0,
+  vieter_heap_empty = 1
+} vieter_heap_error;
+
+/*
+ * Allocate and initialize an empty heap.
+ */
+vieter_heap *vieter_heap_init();
+
+/*
+ * Deallocate a heap.
+ */
+void vieter_heap_free(vieter_heap *heap);
+
+/*
+ * Return how many elements are currently in the heap.
+ */
+uint64_t vieter_heap_size(vieter_heap *heap);
+
+/*
+ * Insert a new value into the heap.
+ */
+vieter_heap_error vieter_heap_insert(vieter_heap *heap, uint64_t key,
+                                     void *data);
+
+/*
+ * Remove the smallest element from the heap.
+ */
+vieter_heap_error vieter_heap_pop(void **out, vieter_heap *heap);
+
+/*
+ * Get the smallest element in the heap without removing it.
+ */
+vieter_heap_error vieter_heap_peek(void **out, vieter_heap *heap);
+
+/*
+ * Acquire a read lock on the heap. Return value is the result of
+ * pthread_rwlock_rdlock.
+ */
+int vieter_heap_rlock(vieter_heap *heap);
+
+/*
+ * Acquire a write lock on the heap. Return value is the result of
+ * pthread_rwlock_wrlock.
+ */
+int vieter_heap_wlock(vieter_heap *heap);
+
+/*
+ * Unlock the lock after having acquired it. Return value is the result of
+ * pthread_rwlock_unlock.
+ */
+int vieter_heap_unlock(vieter_heap *heap);
+
+#endif
diff --git a/src/cron/expression.c b/src/cron/vieter_cron_expression.c
similarity index 100%
rename from src/cron/expression.c
rename to src/cron/vieter_cron_expression.c
diff --git a/src/cron/parse.c b/src/cron/vieter_cron_parse.c
similarity index 99%
rename from src/cron/parse.c
rename to src/cron/vieter_cron_parse.c
index 5c8da06..a82d1c3 100644
--- a/src/cron/parse.c
+++ b/src/cron/vieter_cron_parse.c
@@ -1,4 +1,8 @@
 #include "vieter_cron.h"
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
 
 // This prefix is needed to properly compile
 const uint8_t parse_month_days[] = {31, 28, 31, 30, 31, 30,
diff --git a/src/heap/README.md b/src/heap/README.md
new file mode 100644
index 0000000..8942763
--- /dev/null
+++ b/src/heap/README.md
@@ -0,0 +1,33 @@
+This min-heap implementation is a pretty standard binomial heap.
+
+## Representation in memory
+
+A heap consists of one or more binomial trees, each with a different order `k`
+and `2^k` total nodes. This heap can contain `2^64 - 1` elements at most, which
+is far more than your memory can contain, but it's still fun to mention.
+
+A tree does not have its own memory structure; a node that's the root of a
+binomial tree is simply called the tree.
+
+Each node has the following layout:
+
+```c
+typedef struct vieter_heap_node {
+    uint64_t key;
+    void *data;
+    struct vieter_heap_node *largest_order;
+    union {
+      struct vieter_heap_node *next_tree;
+      struct vieter_heap_node *next_largest_order;
+    } ptr;
+    uint8_t order;
+} vieter_heap_node;
+```
+
+Each node has a pointer to its child with the largest order (if the node's
+order is `0`, this pointer will be NULL). Each non-root node has a pointer to
+its sibling with the next-highest order. These pointers allow the children of a
+binomial tree to be recombined into a new tree, once their root has been
+pop'ed.
+
+Roots point to the binomial tree in the heap with the next largest order.
diff --git a/src/heap/vieter_heap.c b/src/heap/vieter_heap.c
new file mode 100644
index 0000000..b10d94c
--- /dev/null
+++ b/src/heap/vieter_heap.c
@@ -0,0 +1,96 @@
+#include "vieter_heap_internal.h"
+
+#include <stdlib.h>
+
+vieter_heap *vieter_heap_init() {
+  vieter_heap *heap = calloc(1, sizeof(vieter_heap));
+
+  pthread_rwlock_init(&heap->lock, NULL);
+
+  return heap;
+}
+
+uint64_t vieter_heap_size(vieter_heap *heap) {
+  uint64_t size = 0;
+  vieter_heap_node *tree = heap->tree;
+
+  while (tree != NULL) {
+    size |= (uint64_t)1 << tree->order;
+
+    tree = tree->ptr.next_tree;
+  }
+
+  return size;
+}
+
+void vieter_heap_free(vieter_heap *heap) {
+  vieter_heap_node *tree = heap->tree;
+  vieter_heap_node *next;
+
+  while (tree != NULL) {
+    next = tree->ptr.next_tree;
+    vieter_heap_tree_free(tree);
+    tree = next;
+  }
+
+  free(heap);
+}
+
+vieter_heap_error vieter_heap_insert(vieter_heap *heap, uint64_t key,
+                                     void *data) {
+  vieter_heap_node *new_tree = vieter_heap_node_init();
+  new_tree->key = key;
+  new_tree->data = data;
+  new_tree->order = 0;
+
+  if (heap->tree == NULL) {
+    heap->tree = new_tree;
+  } else {
+    heap->tree = vieter_heap_tree_merge(heap->tree, new_tree);
+  }
+
+  return vieter_heap_ok;
+}
+
+vieter_heap_error vieter_heap_pop(void **out, vieter_heap *heap) {
+  if (heap->tree == NULL) {
+    return vieter_heap_empty;
+  }
+
+  heap->tree = vieter_heap_tree_pop(out, heap->tree);
+
+  return vieter_heap_ok;
+}
+
+vieter_heap_error vieter_heap_peek(void **out, vieter_heap *heap) {
+  if (heap->tree == NULL) {
+    return vieter_heap_empty;
+  }
+
+  vieter_heap_node *tree = heap->tree;
+  uint64_t smallest_key = tree->key;
+  *out = tree->data;
+
+  while (tree->ptr.next_tree != NULL) {
+    tree = tree->ptr.next_tree;
+
+    if (tree->key < smallest_key) {
+      smallest_key = tree->key;
+      *out = tree->data;
+    }
+  }
+
+  return vieter_heap_ok;
+}
+
+int vieter_heap_rlock(vieter_heap *heap) {
+  return pthread_rwlock_rdlock(&heap->lock);
+}
+
+int vieter_heap_wlock(vieter_heap *heap) {
+  return pthread_rwlock_wrlock(&heap->lock);
+}
+
+int vieter_heap_unlock(vieter_heap *heap) {
+  return pthread_rwlock_unlock(&heap->lock);
+}
diff --git a/src/heap/vieter_heap_internal.h b/src/heap/vieter_heap_internal.h
new file mode 100644
index 0000000..41850e9
--- /dev/null
+++ b/src/heap/vieter_heap_internal.h
@@ -0,0 +1,8 @@
+#include "vieter_heap.h"
+#include "vieter_heap_tree.h"
+#include <pthread.h>
+
+struct vieter_heap {
+  vieter_heap_node *tree;
+  pthread_rwlock_t lock;
+};
diff --git a/src/heap/vieter_heap_tree.c b/src/heap/vieter_heap_tree.c
new file mode 100644
index 0000000..10c5437
--- /dev/null
+++ b/src/heap/vieter_heap_tree.c
@@ -0,0 +1,192 @@
+#include "vieter_heap_tree.h"
+
+vieter_heap_node *vieter_heap_node_init() {
+  return calloc(1, sizeof(vieter_heap_node));
+}
+
+void vieter_heap_node_free(vieter_heap_node *node) { free(node); }
+
+void vieter_heap_tree_free(vieter_heap_node *root) {
+  if (root->order == 0) {
+    goto end;
+  }
+
+  uint64_t size = 1;
+  vieter_heap_node **stack =
+      malloc(((uint64_t)1 << root->order) * sizeof(vieter_heap_node *));
+  stack[0] = root->largest_order;
+
+  vieter_heap_node *node;
+
+  while (size > 0) {
+    node = stack[size - 1];
+    size--;
+
+    if (node->largest_order != NULL) {
+      stack[size] = node->largest_order;
+      size++;
+    }
+
+    if (node->ptr.next_largest_order != NULL) {
+      stack[size] = node->ptr.next_largest_order;
+      size++;
+    }
+
+    vieter_heap_node_free(node);
+  }
+
+  free(stack);
+
+end:
+  vieter_heap_node_free(root);
+}
+
+vieter_heap_node *vieter_heap_tree_merge_same_order(vieter_heap_node *root_a,
+                                                    vieter_heap_node *root_b) {
+  vieter_heap_node *root, *child;
+
+  if (root_a->key <= root_b->key) {
+    root = root_a;
+    child = root_b;
+  } else {
+    root = root_b;
+    child = root_a;
+  }
+
+  child->ptr.next_largest_order = root->largest_order;
+  root->largest_order = child;
+
+  root->order++;
+
+  return root;
+}
+
+vieter_heap_node *vieter_heap_tree_merge(vieter_heap_node *target_tree,
+                                         vieter_heap_node *other_tree) {
+  vieter_heap_node *out = target_tree;
+
+  vieter_heap_node *next_other_tree, *next_target_tree;
+  vieter_heap_node *previous_target_tree = NULL;
+
+  while (target_tree != NULL && other_tree != NULL) {
+    if (target_tree->order == other_tree->order) {
+      next_other_tree = other_tree->ptr.next_tree;
+      next_target_tree = target_tree->ptr.next_tree;
+
+      target_tree = vieter_heap_tree_merge_same_order(target_tree, other_tree);
+
+      target_tree->ptr.next_tree = next_target_tree;
+
+      // If this merge produces a binomial tree whose size is already in
+      // target, it will be the next target. Therefore, we can  merge target's
+      // trees until we no longer have a duplicate depth.
+      while (next_target_tree != NULL &&
+             next_target_tree->order == target_tree->order) {
+        next_target_tree = next_target_tree->ptr.next_tree;
+        target_tree = vieter_heap_tree_merge_same_order(
+            target_tree, target_tree->ptr.next_tree);
+        target_tree->ptr.next_tree = next_target_tree;
+      }
+
+      if (previous_target_tree != NULL) {
+        previous_target_tree->ptr.next_tree = target_tree;
+      } else {
+        out = target_tree;
+      }
+
+      other_tree = next_other_tree;
+    } else if (target_tree->order > other_tree->order) {
+      next_other_tree = other_tree->ptr.next_tree;
+
+      if (previous_target_tree == NULL) {
+        previous_target_tree = other_tree;
+        out = other_tree;
+      } else {
+        previous_target_tree->ptr.next_tree = other_tree;
+
+        // This single missing line right here broke this entire function for
+        // nearly a week.
+        previous_target_tree = other_tree;
+      }
+
+      other_tree->ptr.next_tree = target_tree;
+      other_tree = next_other_tree;
+    } else {
+      if (previous_target_tree == NULL) {
+        out = target_tree;
+      }
+
+      previous_target_tree = target_tree;
+      target_tree = target_tree->ptr.next_tree;
+    }
+  }
+
+  // Append final part of tree to target
+  if (target_tree == NULL) {
+    previous_target_tree->ptr.next_tree = other_tree;
+  }
+
+  return out;
+}
+
+vieter_heap_node *vieter_heap_tree_pop(void **out, vieter_heap_node *tree) {
+  vieter_heap_node *tree_before_smallest = NULL;
+  vieter_heap_node *previous_tree = NULL;
+  vieter_heap_node *original_root = tree;
+
+  uint64_t smallest_key = tree->key;
+
+  while (tree->ptr.next_tree != NULL) {
+    previous_tree = tree;
+    tree = tree->ptr.next_tree;
+
+    if (tree->key < smallest_key) {
+      smallest_key = tree->key;
+      tree_before_smallest = previous_tree;
+    }
+  }
+
+  vieter_heap_node *tree_to_pop;
+
+  if (tree_before_smallest != NULL) {
+    tree_to_pop = tree_before_smallest->ptr.next_tree;
+    tree_before_smallest->ptr.next_tree = tree_to_pop->ptr.next_tree;
+  } else {
+    tree_to_pop = original_root;
+    original_root = original_root->ptr.next_tree;
+  }
+
+  *out = tree_to_pop->data;
+
+  if (tree_to_pop->order == 0) {
+    vieter_heap_tree_free(tree_to_pop);
+
+    return original_root;
+  }
+
+  // Each child has a pointer to its sibling with the next largest order. If we
+  // want to convert this list of children into their own tree, these pointers
+  // have to be reversed.
+  previous_tree = tree_to_pop->largest_order;
+  vieter_heap_node_free(tree_to_pop);
+
+  tree = previous_tree->ptr.next_largest_order;
+  previous_tree->ptr.next_tree = NULL;
+
+  vieter_heap_node *next_tree;
+
+  while (tree != NULL) {
+    next_tree = tree->ptr.next_largest_order;
+    tree->ptr.next_tree = previous_tree;
+
+    previous_tree = tree;
+    tree = next_tree;
+  }
+
+  // original_root is zero if the heap only contained a single tree.
+  if (original_root != NULL) {
+    return vieter_heap_tree_merge(original_root, previous_tree);
+  } else {
+    return previous_tree;
+  }
+}
diff --git a/src/heap/vieter_heap_tree.h b/src/heap/vieter_heap_tree.h
new file mode 100644
index 0000000..0a299db
--- /dev/null
+++ b/src/heap/vieter_heap_tree.h
@@ -0,0 +1,53 @@
+#ifndef VIETER_HEAP_TREE
+#define VIETER_HEAP_TREE
+
+#include <stdint.h>
+#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;
+} vieter_heap_node;
+
+/*
+ * Allocate and initialize a heap node object.
+ */
+vieter_heap_node *vieter_heap_node_init();
+
+/*
+ * Deallocate a node object.
+ */
+void vieter_heap_node_free(vieter_heap_node *node);
+
+/*
+ * Deallocate a node's entire structure.
+ */
+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);
+
+/*
+ * Given the roots of two trees of the same order, merge them into a heap of one
+ * order larger.
+ */
+vieter_heap_node *vieter_heap_tree_merge_same_order(vieter_heap_node *root_a,
+                                                    vieter_heap_node *root_b);
+
+/*
+ * Remove the smallest element from the given heap.
+ */
+vieter_heap_node *vieter_heap_tree_pop(void **out, vieter_heap_node *root);
+
+#endif
diff --git a/test/heap/test_heap.c b/test/heap/test_heap.c
new file mode 100644
index 0000000..f77b0dc
--- /dev/null
+++ b/test/heap/test_heap.c
@@ -0,0 +1,187 @@
+#include "acutest.h"
+#include "vieter_heap_internal.h"
+#include <stdlib.h>
+
+#define TEST_SIZE(heap, size) \
+    TEST_CHECK(vieter_heap_size(heap) == size); \
+    TEST_MSG("Size: %zu, expected: %lu", vieter_heap_size(heap), (uint64_t)size)
+
+void test_init() {
+    vieter_heap *heap = vieter_heap_init();
+    TEST_CHECK(heap != NULL);
+    TEST_SIZE(heap, 0);
+    vieter_heap_free(heap);
+}
+
+void count_nodes(uint64_t *counter, vieter_heap_node *root) {
+    (*counter)++;
+
+    if (root->largest_order != NULL) {
+        count_nodes(counter, root->largest_order);
+    }
+
+    // This will also traverse the various trees
+    if (root->ptr.next_largest_order != NULL) {
+        count_nodes(counter, root->ptr.next_largest_order);
+    }
+}
+
+uint64_t count_nodes_heap(vieter_heap *heap) {
+    uint64_t counter = 0;
+
+    if (heap->tree != NULL) {
+        count_nodes(&counter, heap->tree);
+    }
+
+    return counter;
+}
+
+void test_insert() {
+    vieter_heap *heap = vieter_heap_init();
+    TEST_SIZE(heap, 0);
+
+    void *data;
+
+    for (uint64_t i = 50; i > 0; i--) {
+        vieter_heap_insert(heap, i, (void *)i);
+        TEST_SIZE(heap, (uint64_t)51 - i);
+        TEST_CHECK(count_nodes_heap(heap) == (uint64_t)51 - i);
+
+        data = 0;
+
+        TEST_CHECK(vieter_heap_peek(&data, heap) == vieter_heap_ok);
+        TEST_CHECK_(data == (void *)i, "%lX == %lX", (uint64_t)data, i);
+    }
+
+    vieter_heap_free(heap);
+}
+
+void test_insert_random() {
+    srand(1);
+
+    vieter_heap *heap = vieter_heap_init();
+    TEST_SIZE(heap, 0);
+
+    uint64_t num = rand();
+    uint64_t smallest = num;
+
+    void *data = NULL;
+
+    for (uint64_t i = 0; i < 5000; i++) {
+        vieter_heap_insert(heap, num, (void *)num);
+        TEST_SIZE(heap, i + 1);
+        TEST_CHECK(count_nodes_heap(heap) == (uint64_t)i + 1);
+
+        if (num < smallest) {
+            smallest = num;
+        }
+
+        TEST_CHECK(vieter_heap_peek(&data, heap) == vieter_heap_ok);
+        TEST_CHECK(data == (void *)smallest);
+
+        data = NULL;
+
+        num = rand();
+    }
+
+    vieter_heap_free(heap);
+}
+
+void test_pop() {
+    const uint64_t n = 500;
+
+    vieter_heap *heap = vieter_heap_init();
+    TEST_SIZE(heap, 0);
+
+    void *data;
+
+    for (uint64_t i = n; i > 0; i--) {
+        vieter_heap_insert(heap, i, (void *)i);
+        TEST_SIZE(heap, (uint64_t)n + 1 - i);
+        TEST_CHECK(count_nodes_heap(heap) == (uint64_t)n + 1 - i);
+
+        TEST_CHECK(vieter_heap_peek(&data, heap) == vieter_heap_ok);
+        TEST_CHECK(data == (void*)i);
+    }
+
+    data = NULL;
+
+    for (uint64_t i = 1; i <= n; i++) {
+        TEST_CHECK(vieter_heap_pop(&data, heap) == vieter_heap_ok);
+        TEST_CHECK(data == (void*)i);
+        TEST_SIZE(heap, (uint64_t)n - i);
+    }
+
+    vieter_heap_free(heap);
+}
+
+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_pop_random() {
+    const uint64_t n = 500;
+
+    srand(0);
+
+    vieter_heap *heap = vieter_heap_init();
+
+    uint64_t *numbers = malloc(n * sizeof(uint64_t));
+    uint64_t num;
+
+    for (uint64_t i = 0; i < n; i++) {
+        num = rand();
+        vieter_heap_insert(heap, num, (void *)num);
+        TEST_SIZE(heap, i + 1);
+        TEST_CHECK(count_nodes_heap(heap) == i + 1);
+
+        numbers[i] = num;
+    }
+
+
+    qsort(numbers, n, sizeof(uint64_t), uint64_t_compare);
+
+    void *data = NULL;
+
+    for (uint64_t i = 0; i < n; i++) {
+        TEST_CHECK(vieter_heap_peek(&data, heap) == vieter_heap_ok);
+        TEST_CHECK_(data == (void *)numbers[i], "peek %lx == %lx", (uint64_t)data, numbers[i]);
+
+        data = NULL;
+
+        TEST_CHECK(vieter_heap_pop(&data, heap) == vieter_heap_ok);
+        TEST_CHECK_(data == (void *)numbers[i], "pop %lx == %lx", (uint64_t)data, numbers[i]);
+        TEST_SIZE(heap, n - i - 1);
+        TEST_CHECK(count_nodes_heap(heap) == n - i - 1);
+
+        // Assure each size is also a valid heap after inserting
+        vieter_heap_insert(heap, numbers[i], (void *)numbers[i]);
+        TEST_SIZE(heap, n - i);
+        TEST_CHECK(count_nodes_heap(heap) == n - i);
+
+        data = NULL;
+
+        TEST_CHECK(vieter_heap_pop(&data, heap) == vieter_heap_ok);
+        TEST_CHECK_(data == (void *)numbers[i], "pop %lx == %lx", (uint64_t)data, numbers[i]);
+        TEST_SIZE(heap, n - i - 1);
+        TEST_CHECK(count_nodes_heap(heap) == n - i - 1);
+    }
+
+    vieter_heap_free(heap);
+    free(numbers);
+}
+
+TEST_LIST = {
+    {"init", test_init},
+    {"insert", test_insert},
+    {"insert random", test_insert_random},
+    {"pop", test_pop},
+    {"pop random", test_pop_random},
+    {NULL, NULL}
+};
diff --git a/test/heap/test_merge.c b/test/heap/test_merge.c
new file mode 100644
index 0000000..10053f2
--- /dev/null
+++ b/test/heap/test_merge.c
@@ -0,0 +1,28 @@
+#include "acutest.h"
+#include "vieter_heap.h"
+#include "vieter_heap_tree.h"
+#include <stdlib.h>
+
+void test_merge_same_order() {
+    vieter_heap_node *root_a = vieter_heap_node_init();
+    root_a->key = 1;
+    root_a->order = 0;
+
+    vieter_heap_node *root_b = vieter_heap_node_init();
+    root_b->key = 2;
+    root_b->order = 0;
+
+    vieter_heap_node *merged = vieter_heap_tree_merge_same_order(root_a, root_b);
+
+    TEST_CHECK(merged == root_a);
+    TEST_CHECK(merged->key == 1);
+    TEST_CHECK(merged->largest_order == root_b);
+    TEST_CHECK(merged->ptr.next_largest_order == NULL);
+
+    vieter_heap_tree_free(merged);
+}
+
+TEST_LIST = {
+    {"merge same order", test_merge_same_order},
+    {NULL, NULL}
+};