diff --git a/Dockerfile b/Dockerfile
index 3de80c1..6c5afc7 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM yolean/node@sha256:e591eac6f5d1f07876bd63bba2bbd1c1218521c5ed5312692851597b47089775
+FROM yolean/node@sha256:9f4a2b32e4ba065ea5471d4d83084d4ba1f860a8bde614518b386999bf0cf9b2
 
 ENV docker_version=17.09.1~ce-0~debian
 ENV compose_version=1.21.0 compose_sha256=af639f5e9ca229442c8738135b5015450d56e2c1ae07c0aaa93b7da9fe09c2b0
diff --git a/README.md b/README.md
index d174931..4f55ecb 100644
--- a/README.md
+++ b/README.md
@@ -6,12 +6,12 @@ Defines a successful build and test run for a microservice, from source to docke
 Invoke build-contract in current folder, use host's docker:
 ```
 docker build --tag yolean/build-contract .
-docker run -v /var/run/docker.sock:/var/run/docker.sock -v $(pwd)/:/source  --rm --name mybuild yolean/build-contract test
+docker run -v /var/run/docker.sock:/var/run/docker.sock -v $(pwd)/:/source  --rm --name mybuild -e PUSH_TAG=testing yolean/build-contract test
 ```
 
 Or for monorepo:
 ```
-docker run -v /var/run/docker.sock:/var/run/docker.sock -v $(pwd)/../:/source -w /source/$(basename $(pwd)) --rm --name mybuild yolean/build-contract test
+docker run -v /var/run/docker.sock:/var/run/docker.sock -v $(pwd)/../:/source -w /source/$(basename $(pwd)) --rm --name mybuild -e PUSH_TAG=testing yolean/build-contract test
 ```
 
 Add `-t` for colors and Ctrl+C support.
diff --git a/build-contract b/build-contract
index bceb3b3..cd7ed1f 100755
--- a/build-contract
+++ b/build-contract
@@ -52,12 +52,6 @@ function wait_for_contract {
   fi
 }
 
-# Perform tests
-BUILD_FLAGS='';
-if [[ $DO_PUSH == true ]]; then
-  BUILD_FLAGS="$BUILD_FLAGS --pull";
-fi
-
 MONOREPO_PRE=$(cat package.json | grep '"build-contract-predockerbuild"' | awk -F '"' '{ print $4 }')
 if [[ "$MONOREPO_PRE" == "#" ]]; then $DIR/nodejs/build-contract-predockerbuild
 elif [[ ! -z "$MONOREPO_PRE" ]]; then npm run build-contract-predockerbuild; fi
@@ -74,8 +68,7 @@ for compose_file in $(ls $CONTRACTS_DIR | grep .yml); do
   # and volumes (including named volumes declared in the docker-compose.yml file)
   $docker_compose down -v
 
-  $docker_compose build $BUILD_FLAGS
-  $docker_compose up --force-recreate -d
+  $docker_compose up --build --force-recreate -d
   $docker_compose logs -f &
   bar=$(wait_for_contract $compose_name)
   echo "  --- build-contract: Build Contract finished with $bar"
diff --git a/nodejs/mnpm.js b/nodejs/mnpm.js
index 8674c82..cf7ee52 100644
--- a/nodejs/mnpm.js
+++ b/nodejs/mnpm.js
@@ -1,6 +1,6 @@
 const fs = require('fs');
 const tar = require('tar-stream');
-const zlib = require('zlib');
+const zlib = require('./zlib-choice');
 
 const tarContentMtime = new Date(946684800000);
 
diff --git a/nodejs/mnpm.spec.js b/nodejs/mnpm.spec.js
index b2c6461..6124df4 100644
--- a/nodejs/mnpm.spec.js
+++ b/nodejs/mnpm.spec.js
@@ -2,7 +2,7 @@ const os = require('os');
 const path = require('path');
 const fs = require('fs');
 const crypto = require('crypto');
-const zlib = require('zlib');
+const zlib = require('./zlib-choice');
 const stream = require('stream');
 const tar = require('tar-stream');
 
@@ -19,13 +19,14 @@ describe("stringifyPackageJson", () => {
 
 describe("Our choice of gzip function", () => {
 
-  it("Is platform independent wrt result checksum", () => {
+  it("Is platform independent wrt result checksum", done => {
     const blob = new stream.PassThrough();
     const sha256 = crypto.createHash('sha256');
     const result = new stream.PassThrough();
     result.on('data', d => sha256.update(d));
     result.on('end', () => expect(sha256.digest('hex')).toBe(
-      'c5f9a2352dadba9488900ba6ede0133270e12350ffa6d6ebbdefef9ee6aa2238'));
+      'b13627bbeee31ae666d6696cf11e411ee6b0e40d4b235cb2a02da32693ba2d3c'));
+    result.on('end', done);
     // Note that this differs from `echo 'x' | gzip - | shasum -a 256 -`
     blob.pipe(zlib.createGzip()).pipe(result);
     blob.end('x\n');
@@ -36,7 +37,7 @@ describe("Our choice of gzip function", () => {
     expect(process.versions.zlib).toBe('1.2.11');
   });
 
-  it("Results may depend on zlib options", () => {
+  it("Results may depend on zlib options", done => {
     const options = {
       windowBits: 14, memLevel: 7,
       level: zlib.constants.Z_BEST_SPEED,
@@ -47,13 +48,13 @@ describe("Our choice of gzip function", () => {
     const result = new stream.PassThrough();
     result.on('data', d => sha256.update(d));
     result.on('end', () => expect(sha256.digest('hex')).toBe(
-      '270b40b49af0dcc1de9631f231d022c93c07f29d2940e14d22ffdd797165e24f'));
-    // Note that this differs from `echo 'x' | gzip - | shasum -a 256 -`
+      'dd8dbe0ba323ab288d9e9272efc1f2bf52f495a812122c6ee9f9c5e7d765fda5'));
+    result.on('end', done);
     blob.pipe(zlib.createGzip(options)).pipe(result);
     blob.end('x\n');
   });
 
-  it("Results may depend on zlib compression level", () => {
+  it("Results may depend on zlib compression level", done => {
     const options = {
       level: zlib.constants.Z_BEST_COMPRESSION
     };
@@ -62,13 +63,13 @@ describe("Our choice of gzip function", () => {
     const result = new stream.PassThrough();
     result.on('data', d => sha256.update(d));
     result.on('end', () => expect(sha256.digest('hex')).toBe(
-      '1437e4b499b5063c9530244d1655dba6986bcbd1258f81f122bdc4c983058ef4'));
-    // Note that this differs from `echo 'x' | gzip - | shasum -a 256 -`
+      '6cda46810118792ed89f1e1662549186b5c851e4ce240be861780bc646e850c6'));
+    result.on('end', done);
     blob.pipe(zlib.createGzip(options)).pipe(result);
     blob.end('x\n');
   });
 
-  it("Results may be more platform independent with no compression", () => {
+  it("Results may be more platform independent with no compression", done => {
     const options = {
       level: zlib.constants.Z_NO_COMPRESSION
     };
@@ -77,12 +78,24 @@ describe("Our choice of gzip function", () => {
     const result = new stream.PassThrough();
     result.on('data', d => sha256.update(d));
     result.on('end', () => expect(sha256.digest('hex')).toBe(
-      '35932a249baf5fe47b9fecaa3482309e447ed8d9b01e207a6ce2846724006784'));
-    // Note that this differs from `echo 'x' | gzip - | shasum -a 256 -`
+      'f2b18200cd38c0d2c3dff4d3e2be9fd83069acd6b73cbc835c708fc3693c45d9'));
+    result.on('end', done);
     blob.pipe(zlib.createGzip(options)).pipe(result);
     blob.end('x\n');
   });
 
+  xit("Results may be better with inflate instead of gzip", done => {
+    const blob = new stream.PassThrough();
+    const sha256 = crypto.createHash('sha256');
+    const result = new stream.PassThrough();
+    result.on('data', d => sha256.update(d));
+    result.on('end', () => expect(sha256.digest('hex')).toBe(
+      'c5f9a2352dadba9488900ba6ede0133270e12350ffa6d6ebbdefef9ee6aa2238'));
+    result.on('end', done);
+    blob.pipe(zlib.createInflate()).pipe(result);
+    blob.end('x\n');
+  });
+
 });
 
 describe("writeProdPackageTgzWithDeterministicHash", () => {
@@ -104,10 +117,10 @@ describe("writeProdPackageTgzWithDeterministicHash", () => {
     const tgz = await fs.promises.readFile(filePath);
     const sha256 = crypto.createHash('sha256');
     sha256.update(tgz);
-    expect(sha256.digest('hex')).toBe('3be69fccaf4716df00adee93c219cfe44f1425aa968d33b6a3a4e725192586be');
+    expect(sha256.digest('hex')).toBe('ebfa2ce786383196d29b927d3f0a51539655ebe56d4bac52b96f7e13749ba79c');
     const sha512 = crypto.createHash('sha512');
     sha512.update(tgz);
-    expect(sha512.digest('base64')).toBe('M24fZ1mSsZYX8dSCGSd54842GgAKd80xInWqNUhSZH1/hx7syKOOx05qMhD8avcFdXNnDMG/N2i/YZJFJNW6rQ==');
+    expect(sha512.digest('base64')).toBe('4aKJrQoeaGZuY8IDk/LmKX9drIVPoeQG00phQ7kZoR+SXHtrgeA19uUnBrclpm4Sm6xIv8/50V5u/dPxWg62Iw==');
     await fs.promises.unlink(filePath);
   });
 
diff --git a/package.json b/package.json
index dc18b76..6eebeb3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "build-contract",
-  "version": "1.5.0",
+  "version": "1.6.0",
   "description": "Defines a successful build and test run for a microservice, from source to docker push",
   "repository": {
     "type": "git",
@@ -23,14 +23,16 @@
     "build-contract-predockerbuild": "./nodejs/build-contract-predockerbuild"
   },
   "engines": {
-    "node": ">=10.1.0"
+    "node": ">=10.2.1"
   },
   "dependencies": {
+    "browserify-zlib": "0.2.0",
+    "pako": "1.0.6",
     "tar-stream": "1.6.1",
     "yamljs": "0.2.8"
   },
   "peerDependencies": {
-    "npm": "6.0.1"
+    "npm": "6.1.0"
   },
   "devDependencies": {
     "jest": "22.4.4"