fix prepending code to builders

src/utils/CodeBuilder.js

@@ -12,33 +12,49 @@ export default class CodeBuilder {
 	addLine ( line ) {
 		if ( this.last === BLOCK ) {
 			this.result += `\n\n${line}`;
-		} else {
+		} else if ( this.last === LINE ) {
 			this.result += `\n${line}`;
+		} else {
+			this.result += line;
 		}
 
 		this.last = LINE;
+		if ( !this.first ) this.first = LINE;
 	}
 
 	addLineAtStart ( line ) {
 		if ( this.first === BLOCK ) {
 			this.result = `${line}\n\n${this.result}`;
-		} else {
+		} else if ( this.first === LINE ) {
 			this.result = `${line}\n${this.result}`;
+		} else {
+			this.result += line;
 		}
 
 		this.first = LINE;
+		if ( !this.last ) this.last = LINE;
 	}
 
 	addBlock ( block ) {
-		this.result += `\n\n${block}`;
+		if ( this.result ) {
+			this.result += `\n\n${block}`;
+		} else {
+			this.result += block;
+		}
 
 		this.last = BLOCK;
+		if ( !this.first ) this.first = BLOCK;
 	}
 
 	addBlockAtStart ( block ) {
-		this.result = `${block}\n\n${this.result}`;
+		if ( this.result ) {
+			this.result = `${block}\n\n${this.result}`;
+		} else {
+			this.result += block;
+		}
 
 		this.first = BLOCK;
+		if ( !this.last ) this.last = BLOCK;
 	}
 
 	isEmpty () {

src/utils/__test__.js

@@ -118,4 +118,55 @@ describe( 'CodeBuilder', () => {
 			// line 4
 		` );
 	});
+
+	it( 'adds a line at start', () => {
+		const builder = new CodeBuilder();
+
+		builder.addLine( '// second' );
+		builder.addLineAtStart( '// first' );
+
+		assert.equal( builder.toString(), deindent`
+			// first
+			// second
+		` );
+	});
+
+	it( 'adds a line at start before a block', () => {
+		const builder = new CodeBuilder();
+
+		builder.addBlock( '// second' );
+		builder.addLineAtStart( '// first' );
+
+		assert.equal( builder.toString(), deindent`
+			// first
+
+			// second
+		` );
+	});
+
+	it( 'adds a block at start', () => {
+		const builder = new CodeBuilder();
+
+		builder.addLine( '// second' );
+		builder.addBlockAtStart( '// first' );
+
+		assert.equal( builder.toString(), deindent`
+			// first
+
+			// second
+		` );
+	});
+
+	it( 'adds a block at start before a block', () => {
+		const builder = new CodeBuilder();
+
+		builder.addBlock( '// second' );
+		builder.addBlockAtStart( '// first' );
+
+		assert.equal( builder.toString(), deindent`
+			// first
+
+			// second
+		` );
+	});
 });