add two tests

negation ~ and missing Init

src/test/java/de/tla2b/prettyprintb/ActionsTest.java

 package de.tla2b.prettyprintb;
 
+import de.tla2b.exceptions.SemanticErrorException;
 import org.junit.Ignore;
 import org.junit.Test;
 
@@ -63,4 +64,15 @@ public class ActionsTest {
 			+ "END";
 		compare(expected, module);
 	}
+
+	@Test(expected = SemanticErrorException.class)
+	public void testMissingInit() throws Exception {
+		final String module = "-------------- MODULE Testing ----------------\n"
+				+ "EXTENDS Naturals \n"
+				+ "VARIABLES x \n"
+				+ "Next == x'=x+1 \n"
+				+ "=================================";
+
+		compare("MACHINE Testing END", module);
+	}
 }

src/test/java/de/tla2b/prettyprintb/LogicOperatorsTest.java

@@ -80,6 +80,19 @@ public class LogicOperatorsTest {
 		compare(expected, module);
 	}
 
+	@Test
+	public void testNegation2() throws Exception {
+		final String module = "-------------- MODULE Testing ----------------\n"
+				+ "CONSTANTS a,b \n"
+				+ "ASSUME a \\in BOOLEAN /\\ b = ~a \n"
+				+ "=================================";
+
+		final String expected = "MACHINE Testing\n"
+				+ "CONSTANTS a, b \n"
+				+ "PROPERTIES a : BOOL & b : BOOL & (a : BOOL & b = bool(not(a = TRUE))) \n" + "END";
+		compare(expected, module);
+	}
+
 	/*
 	 * Implication and Equivalence: =>, \equiv
 	 */