diff --git a/spec/pretty_spec.lua b/spec/pretty_spec.lua
new file mode 100644
index 00000000..85e37706
--- /dev/null
+++ b/spec/pretty_spec.lua
@@ -0,0 +1,40 @@
+local pretty = require("pl.pretty")
+
+describe("pl.pretty.number", function ()
+
+  it("should format memory", function ()
+    local function assert_memory (expected, input)
+      assert.is.equal(expected, pretty.number(input, "M"))
+    end
+    assert_memory("123B", 123)
+    assert_memory("1.2KiB", 1234)
+    assert_memory("10.0KiB", 10*1024)
+    assert_memory("1.0MiB", 1024*1024)
+    assert_memory("1.0GiB", 1024*1024*1024)
+  end)
+
+  it("should format postfixes", function ()
+    local function assert_postfix(expected, input)
+      assert.is.equal(expected, pretty.number(input, "N", 2))
+    end
+    assert_postfix("123", 123)
+    assert_postfix("1.23K", 1234)
+    assert_postfix("10.24K", 10*1024)
+    assert_postfix("1.05M", 1024*1024)
+    assert_postfix("1.07B", 1024*1024*1024)
+  end)
+
+  it("should format postfixes", function ()
+    local function assert_separator(expected, input)
+      assert.is.equal(expected, pretty.number(input, "T"))
+    end
+    assert_separator('123', 123)
+    assert_separator('1,234', 1234)
+    assert_separator('12,345', 12345)
+    assert_separator('123,456', 123456)
+    assert_separator('1,234,567', 1234567)
+    assert_separator('12,345,678', 12345678)
+  end)
+
+
+end)
diff --git a/tests/test-pretty-number.lua b/tests/test-pretty-number.lua
deleted file mode 100644
index 347a5cf5..00000000
--- a/tests/test-pretty-number.lua
+++ /dev/null
@@ -1,33 +0,0 @@
-local test = require 'pl.test'
-local pretty = require 'pl.pretty'
-
-function testm(x,s)
-  test.asserteq(pretty.number(x,'M'),s)
-end
-
-testm(123,'123B')
-testm(1234,'1.2KiB')
-testm(10*1024,'10.0KiB')
-testm(1024*1024,'1.0MiB')
-
-function testn(x,s)
-  test.asserteq(pretty.number(x,'N',2),s)
-end
-
-testn(123,'123')
-testn(1234,'1.23K')
-testn(10*1024,'10.24K')
-testn(1024*1024,'1.05M')
-testn(1024*1024*1024,'1.07B')
-
-function testc(x,s)
-  test.asserteq(pretty.number(x,'T'),s)
-end
-
-testc(123,'123')
-testc(1234,'1,234')
-testc(12345,'12,345')
-testc(123456,'123,456')
-testc(1234567,'1,234,567')
-testc(12345678,'12,345,678')
-