1 files changed, 38 insertions, 0 deletions
diff --git a/sangria-test/src/main/java/com/tavianator/sangria/test/AtomicMatcher.java b/sangria-test/src/main/java/com/tavianator/sangria/test/AtomicMatcher.java
new file mode 100644
index 0000000..03c897e
--- /dev/null
+++ b/sangria-test/src/main/java/com/tavianator/sangria/test/AtomicMatcher.java
@@ -0,0 +1,38 @@
+package com.tavianator.sangria.test;
+
+import com.google.inject.CreationException;
+import com.google.inject.Guice;
+import com.google.inject.Module;
+import com.google.inject.spi.Elements;
+import org.hamcrest.Description;
+import org.hamcrest.TypeSafeDiagnosingMatcher;
+
+/**
+ * Matcher that checks whether a {@link Module} can be installed multiple times.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+final class AtomicMatcher extends TypeSafeDiagnosingMatcher<Module> {
+    @Override
+    protected boolean matchesSafely(Module item, Description mismatchDescription) {
+        // Pass through the SPI to make sure the Module is atomic regardless of its equals() implementation
+        // This ensures atomicity even through Modules.override(), for example
+        Module copy1 = Elements.getModule(Elements.getElements(item));
+        Module copy2 = Elements.getModule(Elements.getElements(item));
+
+        try {
+            Guice.createInjector(copy1, copy2);
+            return true;
+        } catch (CreationException e) {
+            mismatchDescription.appendValue(e);
+            return false;
+        }
+    }
+
+    @Override
+    public void describeTo(Description description) {
+        description.appendText("an atomic Module");
+    }
+}