Add toml-test test suite

.gitattributes

@@ -18,3 +18,6 @@
 *.jar           binary
 *.png           binary
 
+# Exclude toml-test submodule from Github language statistics.
+# See https://github.com/github-linguist/linguist/blob/master/docs/overrides.md
+test-multiple/src/test/resources/toml-test/* linguist-vendored

.gitmodules

@@ -0,0 +1,6 @@
+[submodule "toml/src/test/resources/toml-test"]
+	path = test-multiple/src/test/resources/toml-test
+	url = [email protected]:toml-lang/toml-test.git
+[submodule "test-multiple/src/test/resources/toml-test"]
+	path = test-multiple/src/test/resources/toml-test
+	url = [email protected]:toml-lang/toml-test.git

CONTRIBUTING.md

@@ -62,3 +62,10 @@ Execution failed for task ':japicmp'.
 
      See failure report at file:///home/guillaume/Documents/Projets/night-config/build/reports/japicmp.html
 ```
+
+## Multi-module test suite
+
+The Gradle module `test-multiple` implements tests that require multiple NightConfig modules.
+
+In particular, it executes the tests of [the language agnostic TOML test suite](https://github.com/toml-lang/toml-test).
+To avoid a test dependency on another programming language, we don't run the provided binary, but rather reimplement the tests using the same resources (valid and invalid TOML files).

settings.gradle.kts

@@ -11,3 +11,4 @@ include("toml")
 include("yaml")
 
 include("test-shared")
+include("test-multiple")

test-multiple/build.gradle.kts

@@ -0,0 +1,36 @@
+plugins {
+    `java-library`
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+	api(project(":toml"))
+	api(project(":json"))
+    testImplementation(project(":test-shared"))
+}
+
+// Use Java 11.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(11)
+    }
+}
+
+// Get JUnit5 version from `libs.versions.toml`.
+val versionCatalog = extensions.getByType<VersionCatalogsExtension>().named("libs")
+val junitVersion = versionCatalog.findVersion("junit5")
+    .orElseThrow{ RuntimeException("missing version in libs.versions.toml: junit5") }
+    .getRequiredVersion()
+
+// Use JUnit5.
+testing {
+    suites {
+		val test by getting(JvmTestSuite::class) {
+			useJUnitJupiter(junitVersion)
+		}
+	}
+}