Rework builder interface to only use #run method - close #91

The builder's #run method will be called repeatedly until it returns
true or false. The Builder#wait_for method can be used to cause a
builder to wait for a Thread, Command, or another Builder.

spec/build_tests_spec.rb

@@ -327,6 +327,29 @@ EOF
     expect(`./program.exe`).to eq "The value is 42\n"
   end
 
+  it 'raises an error when a custom builder returns an invalid value from #run' do
+    test_dir("custom_builder")
+    result = run_rscons(rsconscript: "error_run_return_value.rb")
+    expect(result.stderr).to match /Unrecognized MyBuilder builder return value: "hi"/
+    expect(result.status).to_not eq 0
+  end
+
+  it 'raises an error when a custom builder returns an invalid value using Builder#wait_for' do
+    test_dir("custom_builder")
+    result = run_rscons(rsconscript: "error_wait_for.rb")
+    expect(result.stderr).to match /Unrecognized MyBuilder builder return item: 1/
+    expect(result.status).to_not eq 0
+  end
+
+  it 'supports a Builder waiting for a custom Thread object' do
+    test_dir "custom_builder"
+    result = run_rscons(rsconscript: "wait_for_thread.rb")
+    expect(result.stderr).to eq ""
+    expect(result.status).to eq 0
+    expect(lines(result.stdout)).to include "MyBuilder foo"
+    expect(File.exists?("foo")).to be_truthy
+  end
+
   it 'allows cloning Environment objects' do
     test_dir('clone_env')
     result = run_rscons

spec/rscons/builders/simple_builder_spec.rb

@@ -1,12 +0,0 @@
-module Rscons
-  module Builders
-    describe SimpleBuilder do
-      let(:env) {Environment.new}
-
-      it "should create a new builder with the given action" do
-        builder = Rscons::Builders::SimpleBuilder.new({}) { 0x1234 }
-        expect(builder.run(1,2,3,4,5)).to eq(0x1234)
-      end
-    end
-  end
-end

spec/rscons/environment_spec.rb

@@ -230,7 +230,7 @@ module Rscons
     describe "#find_finished_thread" do
       it "raises an error if called with nonblock=false and no threads to wait for" do
         env = Environment.new
-        expect {env.__send__(:find_finished_thread, [], false)}.to raise_error /No threads to wait for/
+        expect {env.__send__(:find_finished_thread, false)}.to raise_error /No threads to wait for/
       end
     end