1 files changed, 28 insertions, 12 deletions
diff --git a/test/-ext-/string/test_capacity.rb b/test/-ext-/string/test_capacity.rb
index df59e76778..2c6c51fdda 100644
--- a/test/-ext-/string/test_capacity.rb
+++ b/test/-ext-/string/test_capacity.rb
@@ -4,27 +4,26 @@ require '-test-/string'
 require 'rbconfig/sizeof'
 
 class Test_StringCapacity < Test::Unit::TestCase
-  def capa(str)
-    Bug::String.capacity(str)
-  end
-
   def test_capacity_embedded
-    size = RbConfig::SIZEOF['void*'] * 3 - 1
-    assert_equal size, capa('foo')
+    assert_equal GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE] - embed_header_size - 1, capa('foo')
+    assert_equal max_embed_len, capa('1' * max_embed_len)
+    assert_equal max_embed_len, capa('1' * (max_embed_len - 1))
   end
 
   def test_capacity_shared
-    assert_equal 0, capa(:abcdefghijklmnopqrstuvwxyz.to_s)
+    sym = ("a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE]).to_sym
+    assert_equal 0, capa(sym.to_s)
   end
 
   def test_capacity_normal
-    assert_equal 128, capa('1'*128)
+    assert_equal max_embed_len + 1, capa('1' * (max_embed_len + 1))
+    assert_equal max_embed_len + 100, capa('1' * (max_embed_len + 100))
   end
 
   def test_s_new_capacity
     assert_equal("", String.new(capacity: 1000))
     assert_equal(String, String.new(capacity: 1000).class)
-    assert_equal(10000, capa(String.new(capacity: 10000)))
+    assert_equal(10_000 - 1, capa(String.new(capacity: 10_000))) # Real capa doesn't account for termlen
 
     assert_equal("", String.new(capacity: -1000))
     assert_equal(capa(String.new(capacity: -10000)), capa(String.new(capacity: -1000)))
@@ -39,21 +38,38 @@ class Test_StringCapacity < Test::Unit::TestCase
   end
 
   def test_literal_capacity
-    s = "I am testing string literal capacity"
+    s = eval(%{
+      # frozen_string_literal: true
+      "#{"a" * (max_embed_len + 1)}"
+    })
     assert_equal(s.length, capa(s))
   end
 
   def test_capacity_frozen
     s = String.new("I am testing", capacity: 1000)
-    s << "fstring capacity"
+    s << "a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE]
     s.freeze
     assert_equal(s.length, capa(s))
   end
 
   def test_capacity_fstring
-    s = String.new("I am testing", capacity: 1000)
+    s = String.new("a" * max_embed_len, capacity: max_embed_len * 3)
     s << "fstring capacity"
     s = -s
     assert_equal(s.length, capa(s))
   end
+
+  private
+
+  def capa(str)
+    Bug::String.capacity(str)
+  end
+
+  def embed_header_size
+    3 * RbConfig::SIZEOF['void*']
+  end
+
+  def max_embed_len
+    GC::INTERNAL_CONSTANTS[:RVARGC_MAX_ALLOCATE_SIZE] - embed_header_size - 1
+  end
 end