add missing test

Author: infeo

src/main/java/org/cryptomator/cryptofs/inuse/RealInUseManager.java

@@ -124,7 +124,6 @@ Properties readInUseFile(Path inUseFilePath) throws IOException, IllegalArgument
 		}
 	}
 
-	//TODO: test
 	UseInfo validate(Properties content) throws IllegalArgumentException {
 		var ownerFromFile = content.getProperty(UseToken.OWNER_KEY);
 		if (ownerFromFile == null || ownerFromFile.isBlank()) {

src/test/java/org/cryptomator/cryptofs/inuse/RealInUseManagerTest.java

@@ -362,7 +362,34 @@ void isInUseChecksUseInfoCache() throws IOException {
 		verify(useInfoCache).get(eq(inUseFilePath), any());
 	}
 
-	//TODO: test validate
+	@Test
+	@DisplayName("validation checks for required properties")
+	void validateChecksForRequiredProperties() {
+		var inUseManager = new RealInUseManager("cryptobot3000", cryptor);
+
+		//owner missing
+		var props = new Properties();
+		Assertions.assertThrows(IllegalArgumentException.class, () -> inUseManager.validate(props));
+
+		//owner is empty
+		props.setProperty(UseToken.OWNER_KEY, "  ");
+		Assertions.assertThrows(IllegalArgumentException.class, () -> inUseManager.validate(props));
+
+		//lastUpdated missing
+		props.setProperty(UseToken.OWNER_KEY, "foobar");
+		Assertions.assertThrows(IllegalArgumentException.class, () -> inUseManager.validate(props));
+
+		//lastUpdated invalid
+		props.setProperty(UseToken.LASTUPDATED_KEY, "3301");
+		Assertions.assertThrows(IllegalArgumentException.class, () -> inUseManager.validate(props));
+
+		//everything good
+		var lastUpdated = Instant.now();
+		props.setProperty(UseToken.LASTUPDATED_KEY, lastUpdated.toString());
+		var useInfo = Assertions.assertDoesNotThrow(() -> inUseManager.validate(props));
+		Assertions.assertEquals("foobar",useInfo.owner());
+		Assertions.assertEquals(lastUpdated, useInfo.lastUpdated());
+	}
 
 	@AfterEach
 	public void afterEach() {