DEV: Move spec/components to spec/lib (#15987)

Lib specs were inexplicably split into two directories (`lib` and `components`)

This moves them all into `lib`.

spec/lib/distributed_memoizer_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe DistributedMemoizer do
+
+  before do
+    Discourse.redis.del(DistributedMemoizer.redis_key("hello"))
+    Discourse.redis.del(DistributedMemoizer.redis_lock_key("hello"))
+    Discourse.redis.unwatch
+  end
+
+  # NOTE we could use a mock redis here, but I think it makes sense to test the real thing
+  # let(:mock_redis) { MockRedis.new }
+
+  def memoize(&block)
+    DistributedMemoizer.memoize("hello", duration = 120, &block)
+  end
+
+  it "returns the value of a block" do
+    expect(memoize do
+      "abc"
+    end).to eq("abc")
+  end
+
+  it "return the old value once memoized" do
+
+    memoize do
+      "abc"
+    end
+
+    expect(memoize do
+      "world"
+    end).to eq("abc")
+  end
+
+  it "memoizes correctly when used concurrently" do
+    results = []
+    threads = []
+
+    5.times do
+      threads << Thread.new do
+        results << memoize do
+          sleep 0.001
+          SecureRandom.hex
+        end
+      end
+    end
+
+    threads.each(&:join)
+    expect(results.uniq.length).to eq(1)
+    expect(results.count).to eq(5)
+
+  end
+
+end