diff --git a/test/lib/main.c b/test/lib/main.c
index 5b5cd7b..9d7503b 100644
--- a/test/lib/main.c
+++ b/test/lib/main.c
@@ -10,10 +10,13 @@
  * Description:
  */
 
-#include "./test-base.h"
+#include "test-base.h"
+
+#include "test-darr.h"
 
 int main(void)
 {
   RUN_TEST_SUITE(test_lib_base);
+  RUN_TEST_SUITE(test_lib_darr);
   return 0;
 }
diff --git a/test/lib/test-darr.h b/test/lib/test-darr.h
new file mode 100644
index 0000000..0a5f007
--- /dev/null
+++ b/test/lib/test-darr.h
@@ -0,0 +1,103 @@
+/* Copyright (C) 2024 Aryadev Chavali
+
+ * You may distribute and modify this code under the terms of the
+ * GPLv2 license.  You should have received a copy of the GPLv2
+ * license with this file.  If not, please write to:
+ * aryadev@aryadevchavali.com.
+
+ * Created: 2024-04-28
+ * Author: Aryadev Chavali
+ * Description: Tests for darr.h
+ */
+
+#ifndef TEST_DARR_H
+#define TEST_DARR_H
+
+#include <lib/darr.h>
+
+#include "../testing.h"
+
+void test_lib_darr_init(void)
+{
+  struct TestCase
+  {
+    size_t n, expected_used, expected_available;
+  } tests[] = {
+      {0, 0, DARR_DEFAULT_SIZE},
+      {10, 0, 10},
+      {2 << 20, 0, 2 << 20},
+  };
+
+  for (size_t i = 0; i < ARR_SIZE(tests); ++i)
+  {
+    darr_t darr = {0};
+#if VERBOSE > 1
+    INFO(__func__, "Testing %lu -> (%lu, %lu)\n", tests[i].n,
+         tests[i].expected_used, tests[i].expected_available);
+#endif
+
+    darr_init(&darr, tests[i].n);
+
+    if (darr.used != tests[i].expected_used ||
+        darr.available != tests[i].expected_available || !darr.data)
+    {
+      FAIL(__func__, "[%lu] -> Expected (%lu, %lu) got (%lu, %lu)\n", i,
+           tests[i].expected_used, tests[i].expected_available, darr.used,
+           darr.available);
+      assert(false);
+    }
+    free(darr.data);
+  }
+}
+
+void test_lib_darr_ensure_capacity_expands(void)
+{
+  struct TestCase
+  {
+    size_t used, available, requested_capacity, expected_available;
+  } tests[] = {
+      // At used,available=1 when requesting one extra we tightly fit
+      {1, 1, 1, 2},
+      // No extraneous allocations when we have enough capacity
+      {0, 10, 1, 10},
+      {7, 10, 2, 10},
+      {1 << 9, 1 << 10, 1, 1 << 10},
+      // When we reallocate we reallocate as much as needed
+      {10, 10, 1, 10 * DARR_REALLOC_MULT},
+      {10, 10, 10, 20},
+      {50, 100, 300, 350},
+      {1 << 20, 2 << 20, 2 << 20, 3 << 20},
+      // When we reallocate we allocate MORE than needed (for
+      // amortized constant)
+      {1, 5, 5, 10},
+      {85, 100, 40, 200},
+      {4 << 20, 5 << 20, 1 << 23, 5 << 21},
+  };
+
+  for (size_t i = 0; i < ARR_SIZE(tests); ++i)
+  {
+    darr_t darr = {0};
+#if VERBOSE > 1
+    INFO(__func__, "Testing (%lu, %lu, %lu) -> %lu\n", tests[i].used,
+         tests[i].available, tests[i].requested_capacity,
+         tests[i].expected_available);
+#endif
+    darr_init(&darr, tests[i].available);
+    darr.used = tests[i].used;
+    darr_ensure_capacity(&darr, tests[i].requested_capacity);
+
+    if (darr.available < tests[i].expected_available || !darr.data)
+    {
+      FAIL(__func__, "[%lu] -> Expected %lu got %lu\n", i,
+           tests[i].expected_available, darr.available);
+      assert(false);
+    }
+
+    free(darr.data);
+  }
+}
+
+TEST_SUITE(test_lib_darr, CREATE_TEST(test_lib_darr_init),
+           CREATE_TEST(test_lib_darr_ensure_capacity_expands), );
+
+#endif