diff --git a/.drone.yml b/.drone.yml
index 1fa30e9..9c3bb17 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -21,7 +21,7 @@ steps:
     image: gcc:12.2.0
     commands:
       - cd algo2/pairingheap
-      - gcc -Wall -Werror -o tests tests.c
+      - gcc -Wall -Werror -o tests pairingheap.c
       - ./tests
   - name: radixheap
     image: gcc:12.2.0
diff --git a/algo2/pairingheap/pairingheap.c b/algo2/pairingheap/pairingheap.c
index d511d25..5c87bfa 100644
--- a/algo2/pairingheap/pairingheap.c
+++ b/algo2/pairingheap/pairingheap.c
@@ -2,6 +2,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "tests.h"
+
 struct PHeapNode {
     int key;
     struct PHeapNode *parent;
@@ -166,3 +168,58 @@ void ph_deinit_free(struct PHeap *ph) {
         free(h);
     }
 }
+
+int cmp_int(const void *a, const void *b) {
+    return *((int *) a) - *((int *) b);
+}
+
+int main() {
+    TEST("consecutive deleteMin calls yield increasing results", {
+        srand(2309);
+    
+        struct PHeap ph;
+        ph_init(&ph);
+
+        for (int i = 0; i < 1000; i++) {
+            ph_insert_malloc(&ph, rand());
+        }
+
+        int max = INT_MIN;
+        while (ph.min != NULL) {
+            struct PHeapNode *h = ph_deletemin(&ph);
+            ASSERT(h->key >= max);
+            max = h->key;
+            free(h);
+        }
+
+        ph_deinit_free(&ph);
+    })
+
+    TEST("deleteMin yields the same order as qsort", {
+        srand(2309);
+
+        struct PHeap ph;
+        ph_init(&ph);
+
+        int n = 1000;
+        int xs[n];
+
+        for (int i = 0; i < n; i++) {
+            xs[i] = rand();
+            ph_insert_malloc(&ph, xs[i]);
+        }
+
+        qsort(xs, n, sizeof(int), cmp_int);
+
+        for (int i = 0; i < n; i++) {
+            struct PHeapNode *h = ph_deletemin(&ph);
+            ASSERT(h->key == xs[i]);
+            free(h);
+        }
+        ASSERT(ph.min == NULL);
+
+        ph_deinit_free(&ph);
+    })
+
+    DONE
+}
diff --git a/algo2/pairingheap/tests.c b/algo2/pairingheap/tests.c
deleted file mode 100644
index 59f9e32..0000000
--- a/algo2/pairingheap/tests.c
+++ /dev/null
@@ -1,86 +0,0 @@
-#include <stdio.h>
-#include <stdlib.h>
-#include <limits.h>
-
-#include "pairingheap.c"
-
-int tests_passed = 0;
-char *current_label;
-int current_num;
-
-#define TEST(LABEL, BLOCK) \
-current_label = LABEL; \
-current_num = __COUNTER__ + 1; \
-BLOCK; \
-fprintf(stderr, "[%3d] \x1b[32m%s ✓\x1b[0m\n", current_num, current_label); \
-tests_passed++;
-
-#define ASSERT(EXPR) \
-if (!(EXPR)) { \
-  fprintf(stderr, "[%3d] \x1b[31m%s ❌\x1b[0m\n", current_num, current_label); \
-  fprintf(stderr, "       Assertion failed in %s:%d:\n", __FILE__, __LINE__); \
-  fprintf(stderr, "       " #EXPR "\n"); \
-  goto after_tests; \
-}
-
-#define DONE \
-after_tests: { \
-  int tests_total = __COUNTER__; \
-  fprintf(stderr, "[\x1b[%dm***\x1b[0m] %d/%d tests passed.\n", tests_passed == tests_total ? 32 : 31, tests_passed, tests_total); \
-  if (tests_passed != tests_total) exit(1); \
-}
-
-int cmp_int(const void *a, const void *b) {
-    return *((int *) a) - *((int *) b);
-}
-
-int main() {
-    TEST("consecutive deleteMin calls yield increasing results", {
-        srand(2309);
-    
-        struct PHeap ph;
-        ph_init(&ph);
-
-        for (int i = 0; i < 1000; i++) {
-            ph_insert_malloc(&ph, rand());
-        }
-
-        int max = INT_MIN;
-        while (ph.min != NULL) {
-            struct PHeapNode *h = ph_deletemin(&ph);
-            ASSERT(h->key >= max);
-            max = h->key;
-            free(h);
-        }
-
-        ph_deinit_free(&ph);
-    })
-
-    TEST("deleteMin yields the same order as qsort", {
-        srand(2309);
-
-        struct PHeap ph;
-        ph_init(&ph);
-
-        int n = 1000;
-        int xs[n];
-
-        for (int i = 0; i < n; i++) {
-            xs[i] = rand();
-            ph_insert_malloc(&ph, xs[i]);
-        }
-
-        qsort(xs, n, sizeof(int), cmp_int);
-
-        for (int i = 0; i < n; i++) {
-            struct PHeapNode *h = ph_deletemin(&ph);
-            ASSERT(h->key == xs[i]);
-            free(h);
-        }
-        ASSERT(ph.min == NULL);
-
-        ph_deinit_free(&ph);
-    })
-
-    DONE
-}
diff --git a/algo2/pairingheap/tests.h b/algo2/pairingheap/tests.h
new file mode 100644
index 0000000..ba98dfd
--- /dev/null
+++ b/algo2/pairingheap/tests.h
@@ -0,0 +1,52 @@
+// single-header unit test framework.
+// if you want to keep your sanity, do not use this.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+
+// globals.
+int tests_passed = 0;
+char *current_label;
+int current_num;
+
+/* Basic idea:
+
+TEST("...", {
+    ASSERT(...)
+    ASSERT(...)
+    ...
+})
+
+
+TEST("...", {
+    ASSERT(...)
+    ASSERT(...)
+    ...
+})
+
+DONE
+
+*/
+
+#define TEST(LABEL, BLOCK) \
+current_label = LABEL; \
+current_num = __COUNTER__ + 1; \
+BLOCK; \
+fprintf(stderr, "[%3d] \x1b[32m%s ✓\x1b[0m\n", current_num, current_label); \
+tests_passed++;
+
+#define ASSERT(EXPR) \
+if (!(EXPR)) { \
+  fprintf(stderr, "[%3d] \x1b[31m%s ❌\x1b[0m\n", current_num, current_label); \
+  fprintf(stderr, "       Assertion failed in %s:%d:\n", __FILE__, __LINE__); \
+  fprintf(stderr, "       " #EXPR "\n"); \
+  goto after_tests; \
+}
+
+#define DONE \
+after_tests: { \
+  int tests_total = __COUNTER__; \
+  fprintf(stderr, "[\x1b[%dm***\x1b[0m] %d/%d tests passed.\n", tests_passed == tests_total ? 32 : 31, tests_passed, tests_total); \
+  if (tests_passed != tests_total) exit(1); \
+}