Add some unit testing for the new model

InvenTree/stock/fixtures/stock.yaml

@@ -70,6 +70,18 @@
     lft: 0
     rght: 0
 
+- model: stock.stockitem
+  pk: 105
+  fields:
+    part: 25
+    location: 7
+    quantity: 1
+    serial: 1000
+    level: 0
+    tree_id: 0
+    lft: 0
+    rght: 0
+
 # Stock items for template / variant parts
 - model: stock.stockitem
   pk: 500

InvenTree/stock/fixtures/stock_tests.yaml

@@ -0,0 +1,31 @@
+- model: stock.stockitemtestresult
+  fields:
+    stock_item: 105
+    test: "Firmware Version"
+    value: "0xA1B2C3D4"
+    result: True
+    date: 2020-02-02
+
+- model: stock.stockitemtestresult
+  fields:
+    stock_item: 105
+    test: "Settings Checksum"
+    value: "0xAABBCCDD"
+    result: True
+    date: 2020-02-02
+
+- model: stock.stockitemtestresult
+  fields:
+    stock_item: 105
+    test: "Temperature Test"
+    result: False
+    date: 2020-05-16
+    notes: 'Got too hot or something'
+
+- model: stock.stockitemtestresult
+  fields:
+    stock_item: 105
+    test: "Temperature Test"
+    result: True
+    date: 2020-05-17
+    notes: 'Passed temperature test by making it cooler'