Add tests

Library/Homebrew/test/dev-cmd/test_spec.rb

@@ -17,4 +17,40 @@ describe "brew test" do
       .and not_to_output.to_stderr
       .and be_a_success
   end
+
+  describe "using inreplace" do
+    it "replaces text in file", :integration_test do
+      install_test_formula "testball", <<~RUBY
+        test do
+          (testpath/"file.txt").write "1"
+          inreplace testpath/"file.txt" do |s|
+            s.gsub! "1", "2"
+          end
+          assert_equal "2", (testpath/"file.txt").read
+        end
+      RUBY
+
+      expect { brew "test", "--verbose", "testball" }
+        .to output(/Testing testball/).to_stdout
+        .and not_to_output.to_stderr
+        .and be_a_success
+    end
+
+    it "fails when assertion fails", :integration_test do
+      install_test_formula "testball", <<~RUBY
+        test do
+          (testpath/"file.txt").write "1"
+          inreplace testpath/"file.txt" do |s|
+            s.gsub! "1", "2"
+          end
+          assert_equal "3", (testpath/"file.txt").read
+        end
+      RUBY
+
+      expect { brew "test", "--verbose", "testball" }
+        .to output(/Testing testball/).to_stdout
+        .and output(/Expected: "3"\n  Actual: "2"/).to_stderr
+        .and be_a_failure
+    end
+  end
 end